Preheat your oven to 375°F (190°C).
Dice the bell pepper and yellow onion into small, uniform pieces.
Heat the olive oil in a skillet over medium heat. Sauté the peppers and onions until they are soft and slightly caramelized, about 5 minutes.
While the vegetables cook, shred the pre-cooked chicken breast into a mixing bowl.
In a small bowl, whisk together the Greek yogurt, half of the enchilada sauce, chili powder, sea salt, and black pepper until smooth.
Fold the shredded chicken and sautéed vegetables into the creamy yogurt mixture.
Cut the corn tortillas into quarters or bite-sized strips.
In a small baking dish, spread a spoonful of the remaining enchilada sauce on the bottom.
Layer half of the tortilla strips, followed by the entire chicken mixture, then the remaining tortilla strips.
Pour the rest of the enchilada sauce over the top and sprinkle evenly with the shredded cheddar cheese.
Bake for 15-20 minutes until the sauce is bubbling and the cheese has melted into a golden crust.
Let the bake rest for 5 minutes before serving to allow the layers to set.