1Heat gas or charcoal grill. In medium bowl, mix beef, salsa and bread crumbs. Shape mixture into 12 (4-inch) patties, 1/4 inch thick. Sprinkle rounded tablespoon cheese in center of 6 patties, spreading slightly. Top with remaining patties; press edges together firmly to seal.
2Place patties on grill over medium heat. Cover grill; cook 11 to 13 minutes, turning once, until meat thermometer inserted in center of patties reads 160°F.
3Place burgers on bottom halves of buns. Top each with tomato and avocado slice and 1 tablespoon sour cream. If desired, top with additional salsa. Cover with top halves of buns.