Slice the flank steak into very thin strips against the grain and place in a small bowl.
Toss the steak with chili powder, ground cumin, sea salt, black pepper, and lime juice until evenly coated.
Heat half of the olive oil in a large cast-iron skillet over medium-high heat.
Sear the steak strips for 3-4 minutes until browned and caramelized, then remove from the pan.
Add the remaining oil to the skillet and sauté the sliced bell peppers and onions for 3 minutes until tender.
Wipe the skillet clean and place the tortilla inside over medium heat.
Sprinkle half of the cheese on one side of the tortilla, then top with the steak and vegetable mixture.
Add the remaining cheese on top and fold the tortilla over to close.
Press down with a spatula and cook for 2 minutes per side until the tortilla is golden-brown and crispy.
Remove from heat, slice into three wedges, and garnish with fresh cilantro.