Preheat your oven to 375°F.
Poach or pan-sear the chicken breast until the internal temperature reaches 165°F, then shred it thoroughly using two forks.
In a medium mixing bowl, combine the shredded chicken, Greek yogurt, 2 tablespoons of the red enchilada sauce, chili powder, cumin, garlic powder, sea salt, and black pepper.
Finely dice the bell pepper and roughly chop the spinach, then fold them into the chicken mixture until evenly distributed.
Slice the corn tortillas into 1-inch wide strips.
In a small oven-safe baking dish, place half of the tortilla strips in an even layer across the bottom.
Spread the chicken and vegetable mixture over the tortilla strips in a single, flat layer.
Top with the remaining tortilla strips, drizzle over the remaining enchilada sauce, and sprinkle with the cheddar cheese.
Bake for 18-20 minutes until the cheese is melted and bubbly and the edges of the tortillas are slightly crisp.
Slice the avocado and place it on top of the bake just before serving.