Slice the flank steak into very thin strips against the grain and place in a bowl.
Toss the steak with chili powder, cumin, garlic powder, sea salt, black pepper, and lime juice until well coated.
Heat the avocado oil in a large cast-iron skillet over medium-high heat.
Add the sliced red bell peppers and onions to the skillet, sautéing for 3-4 minutes until they are tender and have slight charred edges.
Push the vegetables to the side and add the steak strips, searing for 2-3 minutes until browned and cooked to your preference.
Remove the steak and vegetable mixture from the skillet and set aside on a plate.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle half of the Monterey Jack cheese over one half of the tortilla.
Layer the cooked steak, peppers, onions, and fresh cilantro over the cheese, then top with the remaining cheese.
Fold the tortilla in half and press down firmly with a spatula.
Cook for 2 minutes per side until the tortilla is golden brown and crispy and the cheese is fully melted.
Slice into wedges and serve immediately.