chicken enchiladas recipe

- 2 cups cooked, shredded chicken - 1 cup shredded cheese (cheddar, Monterey Jack, or a blend) - 1 small onion, finely chopped - 1 can (10 oz) enchilada sauce - 8 tortillas - 1 cup sour cream - 1/2 cup chopped cilantro (optional) - 1/2 cup sliced black olives (optional) - Salt and pepper to taste