Thinly slice the flank steak against the grain into bite-sized strips.
Thinly slice the bell peppers and red onion into uniform strips.
In a small bowl, combine the ground cumin, chili powder, sea salt, and black pepper.
Toss the steak strips in half of the spice mixture until evenly coated.
Heat the olive oil in a large cast-iron skillet over medium-high heat.
Add the peppers and onions to the skillet and sauté for 3-4 minutes until softened and slightly charred, then remove and set aside.
In the same skillet, sear the steak strips for 2-3 minutes until browned and cooked through, then remove and set aside.
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 cooked steak and pepper mixture.
Top with the remaining cheese and fold the tortilla in half to close.
Cook for 2 minutes per side until the cheese is fully melted and the exterior is perfectly crisp.
Slice into three wedges and serve immediately.