Preheat your oven to 375°F (190°C).
In a small skillet over medium heat, sauté the diced white onion and minced garlic in olive oil until soft and translucent.
Stir in the tomato puree, ancho chili powder, cumin, sea salt, and black pepper, allowing the sauce to simmer for about 5 minutes to develop depth.
In a mixing bowl, toss the cooked shredded chicken breast with 2 tablespoons of the prepared ancho sauce to ensure it stays moist.
Briefly warm the corn tortillas in a dry pan to make them pliable, then dip each one into the sauce to coat both sides.
Fill each tortilla with the chicken mixture, roll tightly, and place them seam-side down in a small baking dish.
Pour the remaining sauce over the tortillas and bake for 15 minutes until the sauce is bubbling.
Remove from the oven and garnish with a dollop of Greek yogurt, fresh chopped cilantro, and sliced scallions before serving.