Preheat oven to 375°F (190°C).
Heat olive oil in a skillet. Add onion and garlic; sauté until softened.
In a bowl, combine shredded chicken with ½ cup enchilada sauce, sautéed onion mixture, and ½ cup cheese.
Fill each tortilla with chicken mixture, roll tightly, and place seam-side down in a greased baking dish.
Pour remaining enchilada sauce over the rolled tortillas. Top with the rest of the shredded cheese.
Bake for 20–25 minutes, until cheese is bubbly and slightly golden.
Garnish with cilantro, sour cream, or avocado slices. Serve hot.