COMBINE cheese and onions. Spoon about 2 Tbsp. cheese mixture onto center of each tortilla; fold in half to completely enclose filling.
COOK, 1 or 2 at a time, in large skillet sprayed with cooking spray on medium-high heat 2 to 3 min. on each side or until crisp and lightly browned on both sides.
CUT into wedges. Serve with salsa.