Slice the flank steak into very thin strips, cutting against the grain for maximum tenderness.
In a small bowl, combine the chili powder, cumin, sea salt, and black pepper, then toss with the steak strips to coat evenly.
Heat the olive oil in a large non-stick skillet over medium-high heat.
Add the sliced red bell pepper and red onion to the skillet, sautéing for 3-4 minutes until softened and slightly charred.
Push the vegetables to the side and add the seasoned steak to the pan, searing for 2-3 minutes until browned and cooked through.
Remove the steak and vegetables from the skillet and set aside on a plate; wipe the skillet clean.
Place the tortilla in the warm skillet and sprinkle the cheddar cheese over one half.
Layer the cooked steak and vegetable mixture over the cheese, then fold the tortilla in half.
Cook for 1-2 minutes per side until the tortilla is golden brown and the cheese has completely melted.
Remove from heat, open slightly to drizzle with lime juice, then slice into wedges and serve immediately.