Preheat the oven to 375°F (190°C) and lightly grease a 9×13 inch baking dish.
Heat 2 tablespoons olive oil in a large skillet over medium heat.
Add the chopped red bell pepper, chopped zucchini, and chopped yellow onion; cook, stirring occasionally, until the vegetables are tender, about 7–10 minutes.
Add the fresh spinach to the skillet and cook until wilted; season the vegetable mixture with salt and pepper to taste.
Spread a thin layer of marinara sauce on the bottom of the prepared baking dish.
Place three no-boil lasagna noodles over the sauce. Spread one-third of the vegetable mixture over the noodles, dollop with about one-third of the ricotta, and sprinkle with about one-third of the shredded mozzarella.
Repeat the layering twice more with sauce, three noodles, vegetables, ricotta and mozzarella, finishing with a top layer of noodles, remaining marinara and the remaining mozzarella.
Cover the dish with aluminum foil and bake for 30 minutes. Remove the foil and bake uncovered for an additional 20 minutes, until the cheese is bubbly and golden.
Let the lasagna stand for 10 minutes before slicing and serving.