Slice the flank steak into thin, bite-sized strips against the grain for maximum tenderness.
In a small bowl, toss the steak strips with the chili powder, ground cumin, sea salt, and black pepper until evenly coated.
Heat the olive oil in a large non-stick skillet over medium-high heat until shimmering.
Add the seasoned steak to the skillet and sear for 3-4 minutes until browned and cooked through, then transfer the meat to a clean plate.
In the same skillet, sauté the thinly sliced bell peppers and onions for 3-5 minutes until they are tender and slightly charred.
Wipe the skillet clean with a paper towel and place the tortilla in the center over medium heat.
Sprinkle half of the shredded cheddar cheese onto one half of the tortilla.
Layer the cooked steak, sautéed vegetables, fresh cilantro, and lime juice over the cheese.
Top with the remaining cheese and fold the tortilla in half to close.
Cook for 2-3 minutes per side, pressing down gently with a spatula, until the tortilla is golden brown and the cheese is fully melted.