Preheat oven to 375°F (190°C).
Poach the chicken breast in simmering water for 12 minutes until cooked through, then shred with two forks.
In a small skillet, heat the olive oil over medium heat and sauté the diced onion and bell pepper until softened.
In a bowl, combine the shredded chicken with the sautéed vegetables and half of the chili powder, cumin, and garlic powder.
In a small saucepan, whisk together the tomato puree with the remaining chili powder, cumin, garlic powder, sea salt, and black pepper, simmering for 3 minutes.
Lightly dip each corn tortilla into the sauce to coat, then fill with the chicken mixture and roll tightly.
Place the rolled tortillas seam-side down in a baking dish, pour the remaining sauce over the top, sprinkle with the shredded cheddar cheese, and bake for 15 to 20 minutes until the cheese is melted and bubbling.