Slice the flank steak into very thin strips against the grain to ensure tenderness.
In a small bowl, toss the steak strips with chili powder, cumin, sea salt, black pepper, and lime juice until evenly coated.
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 they are slightly softened and charred.
Push the vegetables to the outer edges of the pan and add the steak strips to the center, searing for 2 minutes per side until browned.
Remove the steak and vegetable mixture from the pan and set aside, then wipe the skillet clean with a paper towel.
Place the tortilla in the warm skillet and sprinkle the shredded cheddar cheese over one half.
Layer the cooked steak and vegetables over the cheese and fold the tortilla in half to close.
Press down firmly with a spatula and cook for 2 minutes per side until the tortilla is golden-brown and the cheese has melted.
Remove from the heat, sprinkle with fresh cilantro, and slice into three wedges before serving.