Preheat your oven to 375°F and lightly grease a small baking dish.
In a skillet over medium heat, sauté the diced onion and bell pepper in avocado oil until softened and fragrant.
In a medium bowl, combine the shredded chicken with the sautéed vegetables and two tablespoons of the tomato puree.
In a separate small bowl, whisk together the remaining tomato puree, chili powder, ground cumin, garlic powder, sea salt, and black pepper to create the ranchero sauce.
Briefly warm the corn tortillas in a dry skillet or microwave until they are pliable and easy to roll.
Spoon the chicken mixture into the center of each tortilla, roll them up tightly, and place them seam-side down in the prepared baking dish.
Pour the ranchero sauce evenly over the tortillas and sprinkle with the shredded Monterey Jack cheese.
Bake for 15 to 20 minutes until the sauce is simmering and the cheese has melted into a bubbly, golden layer.
Remove from the oven and garnish with fresh cilantro before serving.