Preheat your oven to 375°F (190°C).
In a small saucepan over medium heat, combine the tomato puree, chicken broth, olive oil, ancho chili powder, cumin, garlic powder, and sea salt. Simmer for 5 minutes until slightly thickened.
Finely dice the onion and red bell pepper. Sauté them in a non-stick skillet over medium heat until softened, about 4 minutes.
Add the pre-cooked shredded chicken breast to the skillet with the vegetables and toss with 2 tablespoons of the prepared ancho sauce to moisten.
Warm the corn tortillas in a dry skillet or microwave for 10 seconds until pliable.
Dip each tortilla into the sauce to lightly coat, then fill with the chicken and vegetable mixture. Roll tightly and place seam-side down in a small baking dish.
Pour the remaining ancho sauce over the tortillas and sprinkle evenly with the shredded cheddar cheese.
Bake for 15 minutes until the cheese is melted and the sauce is bubbling.
Garnish with a dollop of nonfat Greek yogurt and freshly chopped cilantro before serving.