Preheat your oven to 375°F.
Heat the olive oil in a skillet over medium heat and sauté the diced red onion and bell pepper until they are softened and fragrant.
In a medium mixing bowl, combine the cooked shredded chicken breast with the sautéed vegetables and half of the chili powder, ground cumin, garlic powder, sea salt, and black pepper.
In a separate small bowl, whisk together the tomato puree with the remaining spices to create a clean red chili sauce.
Spread two tablespoons of the sauce across the bottom of a small oven-safe baking dish.
Briefly warm the corn tortillas in a dry pan to make them pliable, then fill each generously with the chicken mixture and roll them tightly.
Arrange the tortillas seam-side down in the baking dish, pour the remaining sauce over the top, and sprinkle with the shredded sharp cheddar cheese.
Bake for 15 minutes until the cheese is melted and bubbly, then garnish with fresh cilantro before serving.