Boil chicken until they are fully cooked. Shred the chicken once it has cooled down.
Mix your shredded chicken, onion, and can of enchilada sauce together in a bowl. Then in a casserole dish put a layer of tortillas, then a layer of your chicken mix, then a layer of cheese. Repeat this step. Then garnish with black olives.
Put in oven at 350 degrees F for about 1/2 hour or until cheese is melted.