PREPARATION:
- Preheat grill.
- Combine ground beef, onion, thyme, salt and pepper in medium bowl; mix lightly. Shape into eight patties.
- Place cheese in center of four patties to within 1/2 inch of outer edge; top with remaining patties. Press edges together to seal.
- Grill over medium heat, covered, 8 to 10 minutes (or, uncovered, 13 to 15 minutes) to medium (160°F), turning once. Serve with lettuce, tomatoes and Dijon mustard on whole wheat buns, if desired.
