Slice the flank steak into thin, bite-sized strips and season evenly with sea salt, black pepper, garlic powder, and smoked paprika.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Add the steak strips to the hot skillet in a single layer and sear for 2-3 minutes until deeply browned and caramelized, then remove the steak and set aside.
In the same skillet, add the thinly sliced red bell peppers and yellow onions, sautéing for 3-4 minutes until they are tender and slightly charred.
Wipe the skillet clean with a paper towel and return it to medium heat.
Place the whole wheat tortilla in the skillet and sprinkle half of the shredded cheddar cheese over one half of the tortilla.
Layer the seared steak and sautéed vegetables over the cheese, then top with the remaining cheese and fold the tortilla over.
Cook for approximately 2 minutes per side, pressing down gently with a spatula, until the tortilla is golden brown and the cheese is fully melted.
Remove from the skillet, let rest for one minute, and slice into wedges before serving.