Preheat the oven to 375°F. Lightly grease a 9 x 13-inch baking dish.

Bring a large pot of generously salted water to a boil.

Add the lasagna noodles and cook according to the package directions until just tender. Drain and set aside.

Heat the olive oil in a large skillet over medium heat.

Add the diced onion and red bell pepper. Cook for 3 to 4 minutes, stirring occasionally, until they begin to soften.

Add the diced eggplant, zucchini, and yellow squash.

Cook for 8 to 10 minutes, stirring occasionally, until the vegetables begin to soften.

Add the minced garlic and cook for about 30 seconds, stirring constantly, until fragrant.

Stir in the crushed tomatoes, tomato paste, dried basil, oregano, thyme, salt, and black pepper.

Bring the sauce to a gentle simmer and cook for 10 minutes, stirring occasionally, to allow the flavors to combine.

In a medium mixing bowl, combine the ricotta cheese, egg, and Parmesan cheese. Stir until smooth and evenly combined.

Spread a thin layer of the vegetable sauce over the bottom of the prepared baking dish.

Arrange a layer of cooked lasagna noodles over the sauce.

Spread a portion of the ricotta mixture over the noodles.

Spoon a layer of vegetable sauce over the ricotta, then sprinkle with shredded mozzarella cheese.

Repeat the layers of noodles, ricotta filling, vegetable sauce, and mozzarella cheese until the ingredients are used, finishing with vegetable sauce and mozzarella cheese on top.

Cover the baking dish with aluminum foil.

Bake for 35 minutes.

Carefully remove the aluminum foil and return the lasagna to the oven.

Bake uncovered for another 15 to 20 minutes, or until the sauce is bubbling and the mozzarella cheese is melted and lightly golden.

Remove the vegetable lasagna from the oven and let it rest for 10 minutes before slicing.

Sprinkle with chopped fresh basil and serve warm.