Poach the chicken breast in simmering water for 12 minutes until cooked through, then shred finely using two forks.
Dice the onion and bell pepper and sauté them in a skillet with a splash of water until they are soft and translucent.
In a small mixing bowl, whisk together the tomato puree, ancho chili powder, cumin, garlic powder, sea salt, and black pepper.
Combine the shredded chicken and the sautéed vegetables in a bowl with half of the prepared ancho chili sauce.
Warm the corn tortillas in a dry pan for 30 seconds per side to make them pliable, then fill each with the chicken mixture and roll tightly.
Place the rolled tortillas seam-side down in a small baking dish and pour the remaining sauce evenly over the top.
Sprinkle with crumbled feta cheese and bake at 375°F for 15 minutes until the sauce is bubbling and the tortillas are slightly crisp.
Remove from the oven and garnish with fresh chopped cilantro before serving.