Poach the chicken breast in simmering water until cooked through, then shred using two forks.
In a skillet over medium heat, sauté the diced onions, garlic, and bell peppers in avocado oil until soft and fragrant.
Whisk together the tomato puree, chili powder, cumin, sea salt, and black pepper in a small saucepan and simmer for 5 minutes to develop the ranchero flavors.
Lightly warm the corn tortillas, then dip each one into the ranchero sauce to coat.
Fill the center of each tortilla with the shredded chicken and sautéed vegetables, then roll them tightly.
Place the rolls seam-side down in a baking dish, top with the remaining ranchero sauce and shredded cheddar cheese.
Bake at 375°F for 15 minutes until the cheese is melted and bubbly.
Garnish with fresh cilantro and a squeeze of lime juice before serving.