HEAT greased grill to medium-high heat.
MIX meat, 3 Tbsp. mayo and seasoning mix; shape into 12 thin patties. Combine cheese and 2 Tbsp. salsa; spoon onto 6 patties. Cover with remaining patties; pinch edges to seal.
GRILL 7 min. on each side or until done (160ºF). Meanwhile, combine remaining salsa and mayo.
FILL buns with lettuce, tomatoes, burgers and salsa mixture.