Pat the flank steak dry and season both sides evenly with the sea salt, black pepper, chili powder, and garlic powder.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Place the steak in the skillet and sear for approximately 4 minutes per side for medium-rare, then transfer to a cutting board to rest for 5 minutes.
In the same skillet, sauté the sliced bell peppers and red onions for 3 to 5 minutes until they are tender and slightly charred.
Thinly slice the rested steak against the grain into bite-sized strips.
Wipe the skillet clean, place the tortilla flat, and sprinkle half of the cheddar cheese over one half of the tortilla.
Layer the sliced steak and sautéed vegetables over the cheese, top with the remaining cheese, and fold the tortilla over.
Cook for 2 minutes per side over medium heat until the tortilla is golden brown and the cheese is completely melted.