4 boneless, skinless Bowl & Basket chicken breasts (about 6 ounces each)
1/2 cup plus 2 tablespoons Thousand Island dressing
1 medium red onion, cut into 1/2-inch-thick rings
2/3 cup drained refrigerated sauerkraut
4 slices Swiss cheese
Place chicken in large zip-top plastic bag; pour 1/2 cup dressing over chicken. Seal bag, pressing out excess air; massage chicken in bag to coat. Refrigerate at least 2 or up to 4 hours.
Prepare outdoor grill for direct grilling over medium-high heat. Remove chicken from marinade; discard marinade. Spray both sides of onion slices with cooking spray; place chicken and onion on hot grill rack. Cover and cook onion 8 minutes or until grill marks appear, turning once; cook chicken 12 minutes or until internal temperature reaches 165°, brushing with remaining 2 tablespoons dressing and turning once. During last 2 minutes of grilling, top chicken with sauerkraut and cheese; cook 2 minutes or until cheese melts.
Serve chicken topped with grilled onion.