COOK and stir onion in lightly oiled skillet on medium heat to 5 min. or until tender. Add garlic; cook and stir an additional 30 seconds. Place onion mixture in blender container. Add tomatillos, chiles and cilantro; cover. Blend until smooth. Season with salt and pepper to taste, if desired.
HEAT lightly oiled skillet on medium-high heat. Add tortilla strips and chicken; mix lightly. Top with tomatillo sauce and cheese; cover. Cook 3 to 5 min. or until mixture is heated through and cheese is melted.
SERVE hot with refried beans and lime wedges.