Preheat your oven to 375°F (190°C).
Heat olive oil in a small skillet over medium heat and sauté the diced onion until translucent and soft.
In a mixing bowl, combine the cooked shredded chicken breast with the sautéed onions, sea salt, black pepper, and garlic powder.
In a separate bowl, whisk together the tomato puree, minced chipotle peppers, and Greek yogurt until a smooth, creamy sauce forms.
Spread a spoonful of the sauce onto the bottom of a small baking dish.
Warm the corn tortillas slightly to prevent cracking, then dip each one into the sauce to coat.
Fill each tortilla with the chicken mixture, roll tightly, and place seam-side down in the baking dish.
Pour the remaining sauce over the top of the tortillas 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.