Preheat your oven to 375°F (190°C).
Heat the avocado oil in a small saucepan over medium heat and sauté the diced yellow onion until translucent and soft.
Stir in the tomato puree, ancho chili powder, cumin, garlic powder, sea salt, and black pepper; simmer for 5-7 minutes until the sauce thickens slightly.
In a small bowl, combine the cooked shredded chicken breast with 2 tablespoons of the prepared ancho sauce to keep the protein moist.
Warm the corn tortillas in a dry skillet for 30 seconds per side to ensure they are pliable and do not crack when rolling.
Spread a thin layer of the ancho sauce on the bottom of a small oven-safe baking dish.
Place a portion of the chicken mixture into each tortilla, roll them tightly, and arrange them seam-side down in the baking dish.
Pour the remaining ancho chili sauce evenly over the top of the tortillas.
Bake for 12-15 minutes until the sauce is bubbling and the edges of the tortillas are slightly crisp.
Remove from the oven and top with a dollop of plain Greek yogurt and a sprinkle of fresh cilantro before serving.