Heat a large skillet over medium-high heat. Cook and stir pork sausage in the hot skillet until browned and crumbly, about 10 minutes; drain and discard grease.
Transfer sausage to a slow cooker and stir in marinara sauce, green bell pepper, and onion. Poke several holes in each potato with a fork and wrap potatoes in aluminum foil. Push potatoes into sausage mixture.
Cook on Low for 8 hours. Remove and unwrap potatoes, cut in half, and place into a serving bowl; serve sausage mixture over cooked potatoes.