You can also brown the sausage in the slow cooker if it has a sear setting. Place the sausages in slow cooker and add your sliced bell peppers and onions on top. Sprinkle the garlic, Italian seasoning ...
To the same pot, add peppers, onions and garlic ... Braise until tomatoes reduce to a sauce that cloaks peppers, about 10 minutes, adding splashes of water if pot looks dry.