Preheat oven to 375 degrees F (190 degrees C). Grease a 9x13 inch baking dish.
Heat the olive oil in a large skillet over medium heat. Add the onion and garlic and cook until softened, about 5 minutes. Add the broccoli, bell peppers, corn, and diced tomatoes. Cook until the vegetables are tender, about 10 minutes. Remove from heat.
Spread the vegetable mixture into the prepared baking dish. Pour the cream of mushroom soup over the vegetables and stir to combine. Sprinkle with the cheese and bread crumbs.
Bake in the preheated oven for 20 minutes, or until the cheese is melted and the casserole is bubbly.
Interesting Facts
The word "primavera" is Italian for "spring".
This casserole can be served hot, cold, or at room temperature.
This casserole can easily be made vegan by substituting vegan cheese and cream of mushroom soup.