Preheat oven to 350°. In a large skillet, cook sausage over medium heat 4-6 minutes or until no longer pink, breaking into crumbles; drain. Add sauerkraut, peppers and onion; cook and stir 8-10 minutes longer or until vegetables are tender.
Spoon meat mixture onto bun bottoms; place cheese over meat. Replace tops. Place on a baking sheet. Bake 4-6 minutes or until cheese is melted.