Preheat your oven to 375°F (190°C).
In a small skillet, heat the olive oil over medium heat and sauté the diced white onion and bell pepper until they are soft and slightly caramelized.
In a medium bowl, whisk together the tomato puree, water, chili powder, ground cumin, garlic powder, sea salt, and black pepper to create the red chili sauce.
In a separate bowl, combine the cooked shredded chicken breast with the sautéed vegetables and 2 tablespoons of the prepared chili sauce.
Briefly warm the corn tortillas in a dry pan or microwave to make them pliable, then fill each with the chicken mixture and roll them up tightly.
Place the rolled tortillas seam-side down in a small baking dish, then pour the remaining red chili sauce over the top.
Sprinkle the shredded sharp cheddar cheese evenly over the enchiladas and bake for 15 minutes until the sauce is bubbly and the cheese has melted.
Remove from the oven and top with a dollop of nonfat Greek yogurt before serving warm.