Thinly slice the flank steak against the grain into bite-sized strips.
In a small bowl, combine the chili powder, cumin, sea salt, and black pepper, then toss the steak strips in the seasoning until evenly coated.
Heat half of the olive oil in a cast-iron skillet over medium-high heat until shimmering.
Add the sliced bell peppers and red onions to the skillet, sautéing for 3-4 minutes until they are tender-crisp and slightly charred.
Remove the vegetables from the pan and add the remaining olive oil along with the seasoned steak strips.
Sear the steak for 2-3 minutes per side until browned and cooked to your desired doneness, then remove from heat.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle the shredded cheddar cheese over one half of the tortilla, then layer on the cooked steak, peppers, and onions.
Fold the tortilla in half and press down firmly, cooking for 2 minutes per side until the exterior is golden and crispy and the cheese is fully melted.
Remove from the pan, squeeze fresh lime juice over the filling, garnish with chopped cilantro, and slice into wedges.