Preheat oven to 350°F. Grease a 9x13-inch casserole dish.
Heat a large skillet over medium-high heat and add the oil, onion, salt, and pepper. Cook, stirring frequently, for about 5 minutes, until slightly translucent.
Add the garlic and cook while mixing for one more minute or until fragrant. Add the shredded chicken and ⅓ cup (80mL) of enchilada sauce. Stir gently and cook to warm through for 2 to 3 minutes, then set aside. Season with more salt and pepper to taste.
Spoon a few tablespoons of enchilada sauce over a tortilla. Add a generous amount (1/8 the total) of the chicken mixture and top with 2 to 3 tablespoons of cheese. Roll and place in the prepared casserole dish seam-side down. Repeat with the remaining tortillas.
Spoon the remaining enchilada sauce over the tortillas then top with the remaining shredded cheese. Bake for 20 to 30 minutes until the cheese is melted and the enchiladas are warm in the center.
Top with optional toppings before serving, if you like.
Video
Notes
Use a ceramic or glass baking dish. A metal pan can cause the sauce, cheese, and tortillas to turn crisp or hard around the edges and on the bottom. A more insulating dish made of ceramic or glass will bake the enchiladas the best.