Combine soups, onion, salsa and milk. Slice tortillas into 1" strips. In bottom of 9 x 12 baking dish, place 3 T chicken stock. Begin casserole by covering bottom of baking dish with tortilla strips. Add layer of diced chicken. Cover with 1/3 of soup mixture. Repeat the process twice. Top with grated cheese. Bake at 350 for 1 hour. May be made ahead and refrigerated over night.