Thinly slice the flank steak against the grain into bite-sized strips to ensure maximum tenderness.
In a small mixing bowl, toss the steak strips with chili powder, cumin, sea salt, black pepper, and lime juice until evenly coated.
Heat the 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 to 4 minutes until a deep brown crust forms, then remove and set aside.
Add the sliced bell peppers and onions to the same skillet, sautéing for 3 minutes until tender-crisp and slightly charred.
Wipe the skillet clean and place the tortilla inside over medium heat to warm through.
Layer the Monterey Jack cheese on one half of the tortilla, then top with the cooked steak, sautéed vegetables, and fresh cilantro.
Fold the tortilla in half and press down firmly, cooking for 2 minutes per side until the cheese is melted and the exterior is golden and crispy.