Add tomatoes and their juice to a 5- or 6-quart slow cooker. Break apart tomatoes with a spoon. Stir in Italian seasoning, garlic salt and pepper flakes.
Tuck sausages down into sauce. Add potatoes, zucchini and onion. Cover. Cook on high heat for 4 hours or on low heat for 8 hours.
Uncover pot and remove sausages. Slice into 1-inch-thick coins, and return to mixture, stirring gently, along with the bread crumbs. Serve in bowls; sprinkle each with shredded cheese. Makes 6 servings.