Preheat your oven to 375°F.
Heat the avocado oil in a large skillet over medium heat and sauté the diced onion and bell pepper until they are soft and translucent.
Add the shredded chicken, minced garlic, cumin, and half of the chili powder to the skillet, stirring for 2 minutes to combine the flavors.
In a separate small bowl, whisk together the tomato puree, the remaining chili powder, sea salt, and black pepper to create the ranchero sauce.
Briefly warm the corn tortillas in a dry pan or microwave until pliable, then fill each with the chicken and pepper mixture.
Roll the tortillas tightly and place them seam-side down in a small baking dish.
Pour the ranchero sauce evenly over the top of the tortillas and sprinkle with the shredded cheddar cheese.
Bake for 15 minutes until the cheese is melted and bubbly, then garnish with fresh cilantro before serving.