1In 10-inch nonstick skillet, heat oil over medium-low heat until hot. Cook onion in oil 20 to 25 minutes, stirring occasionally, until brown and softened.
2Heat gas or charcoal grill.
3Place bratwurst on grill over medium heat. Cook uncovered 10 to 15 minutes, turning frequently, until hot.
4Wrap each bratwurst with slice of cheese; place on buns. Top with sauerkraut, onion and mustard.