Slice the flank steak into thin strips across the grain and toss them in a small bowl with the chili powder, smoked paprika, sea salt, and black pepper.
Heat the olive oil in a large cast-iron skillet over medium-high heat until shimmering, then add the steak strips in a single layer to sear.
Cook the steak for 3 to 4 minutes until a brown crust forms, then remove the meat from the pan and set it aside on a plate.
In the same skillet, add the sliced bell peppers and red onions, sautéing for 5 minutes until they are tender and have developed slight char marks.
Wipe the skillet clean and place the whole wheat tortilla inside, sprinkling half of the cheddar cheese over one half of the tortilla surface.
Layer the cooked steak and sautéed vegetables over the cheese, top with the remaining cheese, and fold the tortilla in half to close.
Cook for 2 minutes per side until the tortilla is golden and crisp, then remove from heat, squeeze fresh lime juice inside, and garnish with cilantro.