Slice the flank steak against the grain into thin, bite-sized strips.
Dice the red bell pepper and yellow onion into small, uniform pieces.
In a small bowl, combine the sea salt, black pepper, garlic powder, and smoked paprika, then toss with the steak strips to coat.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the steak to the skillet and sear for 2-3 minutes until browned and cooked through, then remove and set aside.
In the same skillet, sauté the peppers and onions for 3-4 minutes until tender and slightly charred.
Wipe the skillet clean and place the tortilla flat; sprinkle half the cheese on one side of the tortilla.
Layer the cooked steak and sautéed vegetables over the cheese, then top with the remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is crisp and the cheese is fully melted.
Slice into wedges and serve immediately while hot.