Preheat the oven to 375°F (190°C).
Cook the lasagna noodles in a large pot of salted boiling water according to package instructions. Drain and set aside.
In a medium saucepan, heat olive oil over medium heat. Add chopped onion and garlic, sauté until onion is translucent.
Add zucchini, yellow squash, and red bell pepper. Cook for 5-7 minutes, until vegetables are tender. Stir in chopped spinach, oregano, basil, salt, and pepper. Remove from heat.
In a mixing bowl, combine ricotta cheese and egg, mixing until smooth.
To assemble the lasagna, spread a thin layer of Alfredo sauce on the bottom of a greased baking dish. Layer 3 lasagna noodles on top.
Spread half of the ricotta mixture over the noodles, followed by half of the veggie mixture and a third of the mozzarella cheese. Add a layer of Alfredo sauce.
Repeat the layering: 3 more noodles, the remaining ricotta mixture, remaining veggie mixture, a third of the mozzarella cheese, and another layer of Alfredo sauce.
Top with the final 3 noodles, the remaining Alfredo sauce, remaining mozzarella cheese, and Parmesan cheese.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes or until the cheese is bubbly and golden brown.
Allow the lasagna to cool for 10 minutes before slicing and serving.