1-Preheat oven to 400 degrees F (200 degrees C). Spread sausage pieces into a baking dish.
2-Bake sausage in preheated oven until heated through, about 20 minutes.
3-Heat olive oil in a large skillet over medium-high heat. Saute onion in oil until translucent, 5 to 7 minutes.
4-Stir sausage with the onion. Pour tomato sauce over the sausage mixture; bring to a simmer and cook for 20 minutes.
5-Stir bell pepper into the mixture to coat in tomato sauce; cook until the bell pepper is tender, about 20 minutes more