Position racks in the upper and lower thirds your oven and preheat the oven to 400 degrees F. Lightly coat 2 large baking sheets with nonstick spray. Lightly mist a 9x13-inch casserole dish with nonstick spray and set aside.
Place the vegetables in a large bowl and drizzle with the olive oil. Sprinkle with salt and pepper, then toss to coat. Divide the vegetables evenly between the two sheets and spread them into a single layer. Roast the vegetables until tender, about 20 minutes, tossing the vegetables on the pan so they cook evenly and switching the pans’ positions on the upper and lower racks once halfway through. Transfer half of the roasted vegetables to the prepared casserole dish and spread into an even layer. Reduce the oven temperature to 350 degrees F.
Meanwhile, in a large mixing bowl, beat the eggs together with the milk, garlic, and Italian seasoning until evenly blended. Gently pour it into the casserole dish. Scatter the remaining vegetables evenly over the top, then dollop the ricotta over the top in small spoonfuls (I like to add about 20 to 24 spoonfuls; you want to each slice to have a few dollops, but have them be large enough so that you can actually taste them).
Bake the casserole for 35 to 40 minutes, until the casserole is golden on top and the center no longer jiggles when you shake the pan. Remove from the oven and sprinkle with fresh herbs. Serve warm.
TO STORE: Cover leftover casserole or store in an airtight storage container and place in the refrigerator for up to 3 days.
TO REHEAT: Rewarm the casserole in the oven at 350 degrees F until hot. You can also gently reheat the casserole in the microwave until warmed through.
TO FREEZE: Store leftover casserole in an airtight, freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.
I like to wrap and freeze individual slices, then thaw them overnight in the refrigerator for quick meals.