Should Kate Middleton be inclined to come over for dinner, I will proudly serve her Oven Roasted Vegetables with Mustard and Warm Lentils.

The best oven roasted vegetables ever for a crowd served on a plate with lentils

Absolutely nothing about this dish is inherently royal—it is a rustic mix of in-season vegetables, a simple sauce, and dirt-cheap green lentils—yet there is a magic in way the oven roasting caramelizes the vegetables and the warm lentils drink up the mustard-olive oil dressing. The combination of the two elevates Oven Roasted Vegetables with Mustard and Warm Lentils from rural to regal.

Oven Roasted Vegetables with Mustard and Warm Lentils combines two of my favorite autumn veggies—acorn squash and cauliflower—with red onions. As they roast, the squash and onion become soft and sweet, and the cauliflower becomes crispy. It’s a veggie texture party, and we’re all invited.

For max flavor, we’re tossing the veggies in stone ground mustard, then whipping up a quick Dijon mustard dressing to toss with the lentils, a.k.a. tasty little flavor sponges. The lentils drink up the dressing for special delivery directly to our taste buds. I recently had the opportunity to try Maille mustard, and I’m all over the double flavor punch the stone ground and Dijon varieties bring to this dish.

Though Oven Roasted Vegetables are a satisfying side dish on their own, pairing them with the warm lentils adds body and elegance. Serve Oven Roasted Vegetables with Mustard and Warm Lentils with simply grilled chicken for a comforting dinner, then enjoy the leftovers the next day for a light lunch.

Dear Kate Middleton, should you happen to be reading this: Consider my dinner invitation to be standing for life. Feel free to bring your husband, your baby, and your best fashion advice. I would be delighted by all three.

A white plate of oven roasted vegetables with lentils

Oven Roasted Vegetables with Mustard and Warm Lentils

A flavorful combination of roasted caramelized acorn squash, cauliflower, and red onions tossed in a mustard vinaigrette with warm lentils.

Prep: 15 mins
Cook: 30 mins
Total: 21 mins

Servings: 4 - 6 servings


  • 3 tablespoons  extra virgin olive oil divided
  • 2 tablespoons  wholegrain mustard
  • 2 teaspoons kosher salt divided
  • 1 teaspoon black pepper divided
  • 2 small red onions cut into 1-inch thick wedges
  • 1 small acorn squash, halved, seeds removed, cut into ½-inch slices
  • 2 cups cauliflower florets (about 8 ounces)
  • 1 cup dried green lentils rinsed
  • 2 cups chicken stock or vegetable stock
  • 1 tablespoon apple cider vinegar
  • 1 tablespoon  Dijon mustard
  • Fresh flat leaf parsley chopped for garnish


  • Place rack in upper third of oven and preheat oven to 425 degrees F. In a large bowl, stir together 2 tablespoons olive oil, wholegrain mustard, 1 teaspoon salt, and 1/2 teaspoon pepper. Place red onion, acorn squash, and cauliflower into the bowl, then gently toss to coat. Place in the oven and roast, turning once, until vegetables are caramelized and tender, about 25 – 30 minutes.
  • Meanwhile, place lentils and stock in a medium saucepan. Bring to a boil, then simmer, covered, until lentils are tender, about 25 minutes.
  • In the same bowl in which you prepared the vegetables (no need to wash), combine remaining 1 tablespoon olive oil, remaining 1 teaspoon salt, remaining 1/2 teaspoon black pepper, apple cider vinegar, and Dijon mustard. Add lentils while still warm and toss to coat. Place on serving platter and top with roasted vegetables. Garnish with fresh parsley.

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Erin Clarke

Hi, I'm Erin Clarke, and I'm fearlessly dedicated to making healthy food that's affordable, easy-to-make, and best of all DELISH. I'm the author and recipe developer here at and of The Well Plated Cookbook. I adore both sweets and veggies, and I am on a mission to save you time and dishes. WELCOME!

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  1. I am going to make some roasted veggies tomorrow too. Roasting makes almost everything taste so much better.

  2. Oh I love love love this recipe Erin! Some of my favorite veggies and with the mustard??? This will be happening soon at our house!

  3. Mustard is amazing! I love that you mixed it with roasted vegetables … definitely fit for royalty! Love the colors!

  4. This is so lovely! I love the way cauliflower gets crispy when roasted and I bet it plays just perfectly against the sweet, buttery squash.

  5. Veggie parties are my favorite! This look so so nice, wow! I’m loving the mustard and lentils addition, what a dish!
    Have a great week, Erin! x

  6. I certainly think royalty would be impressed! I am! I love roasted veggies and I think that the lentils were a lovely addition. Thank you for sharing them Erin!

  7. I love this seasonal squash!! I actually have a roasted squash in the fridge set for a salad tomorrow. Loving the squash/lentil combo though, so I may have to rethink! Gorgeous photos!

  8. I haven’t ever roasted cauliflower before, probably because I don’t buy it very often (GASP), but I think this looks glorious! I, too, loooove acorn squash, and I always love finding new ways to fancy it up!

  9. Erin – love your use of a mustard “sauce” to coat the veggies before roasting – i bet they and the lentils tasted out of this world!
    I just usually throw in veggies with a shake of salt and papper and olive oil – but gotta try your very regal version!

  10. Now this is a side dish that screams beauty in simplicity. Also that mustard sauce sounds delish.

  11. I love the mustard dressing addition to these warm, hearty roasted fall vegetables! A nice reminder that we shouldn’t forget about jazzing up the side dishes a bit more! This would be so delicious for Thanksgiving, too.

  12. Yum, this looks delicious. I adore vegetables of any kind but particularly those that have been roasted in all sorts of yummy things! Hm, what if Kate doesn’t like vegetables? Would she be rejected from the house? ;)

    1. Oh no Laura–I’ll just force feed ’em to her ;-) Or we’ll have tea and cookies. Always good to have a back up plan!

  13. This is really good. I have to ask–why not peel and cube the squash? We found it a bit cumbersome to deal with slices/wedges of squash when everything else is knife-free. Not a criticism, though–delicious and healthy and easy enough to do on a weeknight. Thanks for another great meal, Erin!

    1. Hi Eileen, acorn squash is really difficult to peel, so I find it is quicker and just as delicious to cut it into slices and simply remove the peel while eating. If you prefer, you can leave the peels on, then cut them off before transferring them to a serving plate. I’m so glad you enjoyed the dish!