1. Heat the olive oil in a large skillet (12- to 14-inch diameter works best) over medium heat. Add the sliced sausage and sauté until lightly browned on both sides. Remove to a plate. Add the sliced onions and sauté until starting to soften, about 3 minutes. Stir in the bell peppers, and continue to cook, stirring regularly, until the peppers have begun to soften, about 3 minutes more.
2. Return the sausage to the pan, and then add the diced tomatoes (with juices), Italian seasoning, and a sprinkle of salt and pepper. Stir to combine and continue to cook until the veggies are tender and the tomatoes have thickened slightly, about 5 minutes. Taste and adjust the seasoning if needed.
Sprinkle with Parmesan and fresh parsley, and serve over mashed potatoes, pasta, or with bread of choice.