1large lemonjuice and zest (you should have about 1/4 cup lemon juice total)
Place a rack in the center of your oven, then preheat the oven to 400 degrees F. Generously coat a large, rimmed baking sheet with nonstick spray. Place the potatoes in the center and top with 1 tablespoon olive oil, 1 tablespoon rosemary, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper. Toss to coat, then spread into an even layer. Place in the oven and roast for 20 minutes.
Meanwhile, place the asparagus, chicken, and garlic powder in a large bowl. Drizzle with the lemon juice and add the lemon zest, remaining 2 tablespoons olive oil, 1 tablespoon rosemary, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper. Toss to coat, then transfer to the baking pan with the potatoes. With a spatula, loosely toss the ingredients so that they are evenly combined and spread into an even layer. Overlap the chicken as little as possible.
Return the pan to the oven and bake an additional 15 to 20 minutes, until the chicken is cooked through, stirring once or twice throughout. The asparagus may release some liquid, which you can carefully pour off the pan, or use a slotted spoon or spatula to serve so that you do not get this liquid on your plate. Enjoy hot.
TO STORE: Refrigerate leftovers in an airtight storage container for up to 4 days.
TO REHEAT: Rewarm leftovers on a baking sheet in the oven at 350 degrees F or in the microwave.
TO FREEZE: Freeze leftovers in an airtight freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.