Slice the flank steak into thin, bite-sized strips and toss in a bowl with chili powder, cumin, sea salt, and black pepper.
Heat olive oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the steak strips to the skillet and sear for 3-4 minutes until browned and caramelized on the edges.
Toss in the sliced bell peppers and onions, sautéing for another 3 minutes until the vegetables are tender-crisp.
Squeeze the juice from the lime over the meat and vegetables, then transfer the mixture to a clean plate.
Wipe the skillet clean, place one tortilla in the pan, and sprinkle with half of the Monterey Jack cheese.
Layer the steak and pepper mixture over the cheese, add the remaining cheese, and top with the second tortilla.
Cook for 2-3 minutes per side, pressing down slightly, until the tortillas are golden and the cheese is gooey.
Remove from heat, slice into quarters, and garnish with fresh chopped cilantro.