Add the sausage, bell peppers, onion, marinara, and salt to a 6-quart slow cooker.
Stir to combine, then cover. Cook on high for 4-5 hours or low for 7-8 hours. Do not uncover during this time.
Carefully remove the sausage and slice into 1-inch pieces. Add back to the slow cooker and stir. Taste, and adjust seasoning if desired.
Serve warm on rolls, over pasta, with bread, cooked spaghetti squash, or cauliflower rice.
