Slice the flank steak against the grain into very thin strips.
In a small bowl, toss the steak strips with chili powder, cumin, sea salt, and black pepper 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 cooked through, then remove the steak and set aside.
Add the sliced red bell pepper and red onion to the same skillet, sautéing for 3-4 minutes until they are tender and slightly charred.
Wipe the skillet clean and return to medium heat; place the tortilla in the pan.
Sprinkle half of the cheese over one side of the tortilla, then layer on the cooked steak, sautéed peppers, onions, and the remaining cheese.
Fold the tortilla in half and press down firmly with a spatula.
Cook for 2 minutes per side until the tortilla is crispy and the cheese is fully melted.
Remove from heat, squeeze the fresh lime juice over the filling, and garnish with chopped cilantro before slicing into wedges.