Preheat your oven to 400°F. Toss zucchini, bell peppers, mushrooms, and onion with olive oil, garlic, Italian seasoning, salt, and pepper. Spread on a baking sheet and roast for 15–20 minutes, until tender and slightly caramelized.
In a medium saucepan, heat 2 tablespoon olive oil over medium heat. Add chopped onion and sauté until soft, about 5 minutes. Add garlic and cook for 1 minute more. Stir in crushed tomatoes, salt, and pepper. Simmer on low heat for 15–20 minutes, stirring occasionally.
In a large mixing bowl, combine ricotta cheese, Parmesan, egg, Italian seasoning, salt, and pepper. Give it a good mix.
Now it is time to put the lasagna together. Spread 1 cup of marinara sauce on the bottom of a 9×13-inch lasagna pan. Layer 4 lasagna noodles on top of the sauce. Spread ¼ of the ricotta mixture over the noodles. Add ¼ of the roasted vegetables. Sprinkle 1 cup mozzarella cheese over the veggies and add a scoop or two of sauce on top of the veggies. Repeat: noodles, ricotta mixture, vegetables, mozzarella, and sauce. Continue until all the ingredients are gone and then top with sauce mozzarella cheese. I was able to get 4 layers of 4 lasagna noodles on each layer.
Bake at 375°F for 30-40 minutes or until the cheese is golden and bubbly.
Allow the lasagna to rest 10–15 minutes on a rack before slicing. This helps the layers set and makes for perfect slices. Garnish with fresh basil or parsley if you would like.