Preheat oven to 375°F (190°C).
Place chicken breast in a pot of simmering water for 12-15 minutes until cooked through, then shred with two forks.
Heat avocado oil in a small pan over medium heat and sauté diced red onion until translucent.
In a small bowl, whisk together tomato puree, chili powder, cumin, garlic powder, sea salt, and black pepper to create the sauce.
Toss the shredded chicken with 2 tablespoons of the red chili sauce and the sautéed onions.
Warm the corn tortillas slightly, fill each with the chicken mixture, roll tightly, and place seam-side down in a baking dish.
Pour the remaining sauce over the tortillas and sprinkle with shredded cheddar cheese.
Bake for 15-20 minutes until the cheese is bubbly and the edges are slightly crisp.
Garnish with fresh cilantro before serving.