Preheat your oven to 375°F and lightly grease a small baking dish with a touch of olive oil.
In a small skillet over medium heat, add the olive oil and sauté the finely diced white onion until translucent and fragrant.
Stir in the ancho chili powder, cumin, garlic powder, sea salt, and black pepper, cooking for 30 seconds to toast the spices and release their oils.
Pour in the tomato puree and a splash of water, simmering for 5 minutes until the sauce thickens into a rich consistency.
In a medium bowl, toss the cooked and shredded chicken breast with two tablespoons of the prepared ancho sauce to ensure every bite is flavorful.
Briefly warm the corn tortillas in a dry pan or microwave for 15 seconds to make them pliable for rolling without cracking.
Place a portion of the seasoned chicken mixture into each tortilla, roll tightly, and arrange them seam-side down in the baking dish.
Pour the remaining ancho chili sauce over the center of the enchiladas and sprinkle evenly with the shredded sharp cheddar cheese.
Bake for 15 minutes until the sauce is bubbling and the cheese has melted into a golden crust.
Garnish with freshly chopped cilantro before serving warm.