Slice the flank steak into thin, bite-sized strips and place them in a small bowl.
Season the steak strips with cumin, chili powder, sea salt, and black pepper, tossing 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 in a single layer and sear for 2-3 minutes until browned and caramelized; remove from the pan.
In the same skillet, sauté the sliced bell peppers and red onion for 3-4 minutes until they are tender-crisp.
Wipe the skillet clean and place the whole wheat tortilla inside over medium heat.
Sprinkle half of the Monterey Jack cheese over one side of the tortilla, then layer on the steak and sautéed vegetables.
Top with the remaining cheese and fold the tortilla in half.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately.