In a small bowl, combine the chili powder, cumin, smoked paprika, sea salt, and black pepper.
Pat the flank steak dry with a paper towel and rub the spice mixture evenly over both sides.
Heat the olive oil in a cast-iron skillet over medium-high heat.
Add the sliced red bell pepper and yellow onion to the skillet, sautéing for 3-4 minutes until they are softened and slightly charred.
Push the vegetables to the side of the pan and add the steak. Sear for 3 minutes per side for medium-rare, or until it reaches your desired doneness.
Remove the steak from the pan and let it rest for 5 minutes before slicing into thin strips against the grain.
Toss the sliced steak with the lime juice to brighten the flavors.
Wipe out the skillet and place the tortilla in the pan over medium heat.
Sprinkle half of the cheddar cheese over one half of the tortilla, then layer on the steak, peppers, and onions.
Top with the remaining cheese and fold the tortilla in half.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese is completely melted.
Slice into wedges and garnish with fresh cilantro before serving.