In a small bowl, combine smoked paprika, cumin, garlic powder, sea salt, and black pepper.
Rub the spice mixture evenly over both sides of the flank steak and drizzle with lime juice.
Heat a grill pan or cast-iron skillet over medium-high heat with the avocado oil.
Add the steak to the hot pan and cook for 4-5 minutes per side for medium-rare, then remove and let rest for 5 minutes.
While the steak rests, sauté the sliced bell peppers and onions in the same pan until they are tender and slightly charred.
Thinly slice the rested steak against the grain into bite-sized strips.
Place the tortilla in the pan, sprinkle half of the cheese on one side, then layer the steak and sautéed vegetables on top.
Add 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.