Preheat your oven to 375°F (190°C) and lightly grease a small baking dish.
Poach or grill the chicken breast until fully cooked, then shred it using two forks.
In a small skillet, heat the avocado oil over medium heat and sauté the diced white onion until soft and translucent.
In a mixing bowl, combine the shredded chicken, sautéed onion, sea salt, black pepper, chili powder, and 2 tablespoons of the red enchilada sauce.
Briefly warm the corn tortillas in a dry pan or microwave to make them pliable.
Place a portion of the chicken mixture into each tortilla, roll tightly, and place seam-side down in the baking dish.
Pour the remaining red enchilada sauce over the tortillas and sprinkle evenly with the Monterey Jack cheese.
Bake for 15-20 minutes until the sauce is bubbling and the cheese has melted perfectly.
Garnish with freshly chopped cilantro before serving.