Mix sour cream and salsa until blended. Cook and stir onions and garlic in hot oil in large skillet on medium heat 4 to 5 min. or until onions are crisp-tender. Stir in chicken, 1 cup sour cream mixture, 1/2 cup cheese and chiles.
Spoon about 1/3 cup chicken mixture down center of each tortilla; roll up. Place, seam-sides down, in 13x9–inch baking dish sprayed with cooking spray. Top with remaining sour cream mixture and cheese. Cover.
Bake 15 to 20 min. or until heated through.