Preheat your oven to 375°F (190°C) and lightly grease a small baking dish with a touch of cooking spray.
In a medium skillet over medium heat, sauté the diced white onion and green bell pepper for 4-5 minutes until the vegetables are tender.
In a mixing bowl, combine the cooked shredded chicken breast with the sautéed vegetables, sea salt, black pepper, and chili powder, tossing well to distribute the spices.
To make the tortillas pliable, wrap them in a damp paper towel and microwave for 20 seconds, or quickly warm them in a dry skillet for 30 seconds per side.
Lay each tortilla flat, place half of the chicken and vegetable mixture in the center, and roll them up tightly.
Place the rolled tortillas seam-side down in the prepared baking dish.
Pour the red enchilada sauce evenly over the tortillas, ensuring the edges are covered to prevent them from drying out during baking.
Sprinkle the shredded sharp cheddar cheese over the top of the sauce.
Bake for 15-20 minutes, or until the sauce is bubbling and the cheese has completely melted.
Remove from the oven and let cool for 5 minutes before topping with a dollop of Greek yogurt and fresh cilantro.