Cook chicken, remove skin and bones, and cut into large bite-sized pieces. Saute onion in small amount of oil. Add chiles, soup and half of the grated cheese. Cook slowly until cheese melts. Line a buttered 6 x 10-inch casserole with tortilla pieces. Layer with half the chicken, then half the cheese sauce. Repeat layers. Top with remaining grated cheese. Baked at 325 degrees for 45 to 60 minutes, until heated all the way through.
SERVES: 4 - 6