1. Combine Ground Beef, walnuts, salt, pepper, and in a medium bowl, mixing lightly but thoroughly. Lightly shape into four 1/2-inch thick patties.
2. Place patties on grid over medium, ash-covered coals. Grill, covered, 8 to 10 minutes (over medium heat on preheated gas grill, covered, 7 to 9 minutes) until instant-read thermometer inserted horizontally into center registers 160°F, turning occasionally.
3. Place two apple rounds on bottom of each roll; top with burger. Evenly spread cheese and preserves over burgers. Close sandwiches.
Test Kitchen Tips Cooking times are for fresh or thoroughly thawed ground beef. Color is not a reliable indicator of ground beef doneness.
Apple rounds may be grilled for 3 to 4 minutes, if desired.