Preheat the oven to 375 degrees F and grease a 9x13-inch baking dish.

Bring a large pot of salted water to a boil. Cook the lasagna noodles until just tender, then drain and set them aside.

Heat the olive oil in a large skillet over medium heat. Add the onion and bell pepper and cook 3 to 4 minutes, until softened.

Add the eggplant, zucchini, and yellow squash. Cook 8 to 10 minutes, stirring now and then, until the vegetables soften and shrink down.

Stir in the garlic and cook 30 seconds, just until fragrant.

Add the crushed tomatoes, tomato paste, dried basil, oregano, thyme, salt, and black pepper. Simmer 10 minutes, until the sauce thickens.

In a medium bowl, stir the ricotta cheese, egg, and Parmesan cheese together until smooth.

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

Add a layer of noodles, then the ricotta mixture, more vegetable sauce, and shredded mozzarella.

Repeat the layers, finishing with vegetable sauce and mozzarella on top.

Cover the dish with foil and bake for 35 minutes.

Remove the foil and bake 15 to 20 minutes more, until the cheese is melted and lightly browned.

Let the lasagna rest for 10 minutes before slicing. Sprinkle with fresh basil and serve.