Cook chiles in boiling water in medium saucepan 10 min. or until tender; drain, reserving 1/2 cup of the cooking water. Blend chiles, reserved water, onions and garlic in blender until smooth.
Heat oil in large skillet on medium heat. Add tortilla strips; cook 5 min. or until golden brown but not crisp, stirring occasionally.
Add chile sauce and chicken to skillet; cook 5 min. or until heated through, stirring occasionally. Sprinkle with cheese; cover. Cook 5 min. or until cheese is melted.