Slice the flank steak into thin, bite-sized strips against the grain.
In a small bowl, toss the steak strips with chili powder, cumin, sea salt, black pepper, and lime juice until evenly coated.
Heat the avocado oil in a large non-stick skillet over medium-high heat.
Add the steak to the skillet and sear for 3-4 minutes until browned and cooked through, then remove from the pan and set aside.
In the same skillet, sauté the thinly sliced red bell pepper and red onion for 3 minutes until they begin to soften.
Wipe the skillet clean and return it to medium heat.
Place the tortilla in the skillet, sprinkle the cheddar cheese over one half, and top with the cooked steak and sautéed vegetables.
Fold the tortilla in half and press down firmly with a spatula.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.
Remove from heat, garnish with fresh cilantro, and slice into three wedges before serving.