Preheat the oven to 350°F. Meanwhile, place a large skillet over medium-high heat. Add the oil and chopped onions and cook until they are softened.
Add the garlic and sauté for another minute. Add the shredded chicken and 1 cups of enchilada sauce.
Bring the mixture to a simmer and cook until the chicken is heated through. Remove it from the heat.
Divide the chicken mixture evenly onto 8 flour tortillas. Spread it out in the middle, then sprinkle about 1/4 cup of cheese over the chicken mixture on each tortilla. Roll the tortillas up.
Pour 1/2 cup of enchilada sauce into a 9x13 inch baking dish to cover the bottom of the pan. Place the rolled up tortillas into the pan seam-side down.
Pour the remaining 1/2 cup of enchilada sauce on top and brush it evenly over the tortillas. Sprinkle the remaining 2 cups of cheese on top.
Cover the dish with aluminum foil and bake the enchiladas for 15 minutes. Take the foil off, then bake for an additional 10 minutes, or until the sauce is bubbly and the cheese has melted.
Serve the enchiladas warm with your favorite toppings and enjoy!