Sauté the onion and garlic in olive oil over medium-high heat for 3-5 minutes until softened. Add your chosen chopped veggies and cook for 7-10 minutes until tender-crisp. Set aside.
In a bowl, whisk the egg into the ricotta cheese. Stir in the fresh spinach until just combined.
Spread a thin layer of tomato sauce on the bottom of a greased 9x13 inch baking dish. Layer with 4 lasagna noodles, half of the ricotta-spinach mixture, half of the cooked vegetables, and 3/4 cup of tomato sauce.
Repeat the layering process: another 4 noodles, the remaining ricotta mixture, the remaining veggies, and 3/4 cup sauce. Top the entire pan with the final 4 noodles, remaining sauce, and shredded mozzarella cheese.
Cover the baking dish tightly with foil.
Bake in a preheated oven at 375°F (190°C) for 40 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is melted, bubbly, and lightly golden.