Prep the chiles: Warm a dry skillet over medium heat. Toast guajillo and ancho chiles for 30–45 seconds per side until fragrant.
Don’t burn them.
Soften the chiles: Place toasted chiles in a bowl and cover with hot water. Soak 15 minutes until pliable. Drain.
Blend the sauce: In a blender, add soaked chiles, onion, garlic, tomato, chicken broth, cumin, oregano, and vinegar.
Blend until very smooth. Add a splash more broth if too thick.
Cook the sauce: Heat oil in a saucepan over medium. Pour in the blended sauce through a fine mesh sieve if you want it extra silky.
Simmer 8–10 minutes. Season with salt. The sauce should coat a spoon.
Warm the tortillas: In a skillet, add a thin film of oil.
Quickly toast each tortilla 10–15 seconds per side until pliable. Stack and keep warm under a clean towel.
Prep the filling: Toss shredded chicken with a few spoonfuls of warm chile sauce to moisten. Mix in chopped onion if using.
Assemble: Preheat oven to 375°F (190°C).
Spread a thin layer of sauce in a baking dish. Dip each tortilla lightly in sauce, fill with chicken, roll, and place seam-side down in the dish.
Sauce and cheese: Pour remaining sauce over the enchiladas, making sure they’re well coated. Top evenly with shredded Oaxaca cheese.
Bake: Bake 12–15 minutes until the cheese is melted and bubbling.
Broil 1–2 minutes if you want golden spots.
Finish: Rest 5 minutes. Garnish with cilantro and serve with lime wedges.