In the slow cooker, this recipe can take anywhere from 3-5 hours to cook, plus about 15 minutes of prep. If you don't have that kind of time or you don't own a slow cooker, you can cook it on the stovetop in about an hour. Brown the sausage and sliced onions in a little olive oil in a large, heavy bottomed soup pot or dutch oven for about 6 minutes oven medium-high heat. Pour in the marinara and add sliced peppers and seasonings. Stir it all together and bring to a boil. Cover and simmer for at least 45 minutes to an hour.