Slice the flank steak against the grain into very thin strips.
In a small bowl, whisk together the lime juice, chili powder, cumin, sea salt, and black pepper.
Toss the steak strips in the lime marinade 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 2-3 minutes until browned and slightly charred; remove the steak and set aside.
In the same skillet, add the sliced bell peppers and red onions, sautéing for 3-4 minutes until they are tender and slightly caramelized.
Wipe the skillet clean and place the tortilla in the center over medium heat.
Sprinkle half of the cheddar cheese on one half of the tortilla, then layer on the cooked steak, sautéed vegetables, and fresh cilantro.
Top with the remaining cheese and fold the tortilla in half.
Cook for 2 minutes per side, pressing down slightly with a spatula, until the tortilla is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately.