Heat the olive oil in a large skillet over medium heat. Add the onion and sauté until softened, about 5 minutes. Add the garlic and cook for 1 minute.
Add the crushed tomatoes and oregano and season with salt and pepper. Simmer for 10 minutes.
Add the chopped basil and stir to combine. Remove from heat.
Spread the cooked polenta in an even layer in a 9x13 inch baking dish. Top with the sausage slices and spread the tomato sauce over the top. Sprinkle with Parmesan cheese and mozzarella cheese.
Bake in the preheated oven for 25 minutes, or until the cheese is melted and bubbly.
Serve hot.
Interesting Facts
Polenta is a traditional Italian dish made from cornmeal.
It can be served as a main dish or side dish.
It can also be used as a base for other dishes, such as this baked polenta with sausage.