Slice the flank steak into very thin strips across the grain to ensure tenderness.
Thinly slice the bell peppers and red onion into strips of similar size.
In a small bowl, whisk together the sea salt, black pepper, garlic powder, and smoked paprika.
Toss the steak strips in the spice mixture until every piece is evenly coated.
Heat the avocado oil in a large cast-iron skillet or non-stick pan over medium-high heat.
Add the steak to the skillet and sear for 2-3 minutes until deeply browned; remove the steak and set it aside on a plate.
In the same skillet, sauté the peppers and onions for 3-4 minutes until they are tender-crisp and slightly caramelized.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle half of the cheddar cheese on one side of the tortilla, top with the steak and vegetable mixture, and cover with the remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side until the cheese is fully melted and the exterior is golden brown and crispy.