Preheat your oven to 375°F (190°C).
In a small saucepan over medium heat, add the olive oil, ancho chili powder, cumin, and garlic powder, stirring for 30 seconds until the spices are fragrant.
Stir in the tomato puree and a splash of water, then simmer for 5 minutes before seasoning with sea salt and black pepper.
In a medium bowl, combine the shredded cooked chicken breast with the diced yellow onion and 2 tablespoons of the prepared ancho sauce.
Briefly warm the corn tortillas in a dry skillet over medium heat until they are soft and pliable.
Place half of the chicken mixture into each tortilla, roll them tightly, and place them seam-side down in a small oven-safe baking dish.
Pour the remaining ancho chili sauce over the top of the tortillas and sprinkle evenly with the shredded cheddar cheese.
Bake for 15 minutes or until the cheese is melted and the sauce is bubbling around the edges.
Remove from the oven and top with a dollop of Greek yogurt and fresh chopped cilantro before serving.