Thinly slice the flank steak against the grain into bite-sized strips.
In a small bowl, whisk together the chili powder, cumin, smoked paprika, sea salt, black pepper, and lime juice.
Toss the steak strips in the spice mixture until evenly coated.
Heat the olive oil in a large non-stick skillet over medium-high heat.
Add the sliced onions and bell peppers to the skillet, sautéing for 3-4 minutes until they are tender and slightly charred.
Push the vegetables to the side and add the steak strips, searing for 2-3 minutes until browned and cooked through.
Remove the steak and vegetables from the skillet and set aside.
Wipe the skillet clean and place the corn tortillas inside over medium heat.
Evenly distribute the Monterey Jack cheese onto the tortillas, followed by the steak and vegetable mixture and fresh cilantro.
Fold the tortillas in half and cook for 1-2 minutes per side until the cheese is melted and the tortillas are golden and crisp.