Preheat your oven to 375°F and lightly grease a small baking dish with a touch of oil.
In a small skillet over medium heat, sauté the finely diced yellow onion in olive oil until translucent and fragrant.
In a bowl, whisk together the tomato puree, chili powder, cumin, garlic powder, sea salt, and black pepper to create a clean red chili sauce.
Shred the cooked chicken breast and combine it with 2 tablespoons of the prepared sauce in a mixing bowl until evenly coated.
Warm the corn tortillas in a dry pan for 30 seconds per side until pliable so they do not crack when rolling.
Place a portion of the chicken mixture in the center of each tortilla, roll them up tightly, and arrange them seam-side down in the baking dish.
Top the tortillas with the remaining red chili sauce and a layer of shredded sharp cheddar cheese.
Bake for 15 minutes until the cheese is melted and the sauce is bubbling around the edges.
Finish with a sprinkle of fresh cilantro and serve immediately while hot.