Slice the flank steak into thin strips across the grain and season with sea salt, black pepper, and garlic powder.
Heat avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the steak strips to the skillet and sear for 2-3 minutes until browned and juicy, then remove from the pan.
In the same skillet, sauté the sliced bell peppers and onions for 3-4 minutes until they are tender and slightly charred.
Wipe the skillet clean and place the tortilla inside over medium heat.
Sprinkle half the cheese on one side of the tortilla, then layer the steak, peppers, onions, and remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is golden brown and the cheese is fully melted.
Remove from heat, let rest for one minute, then slice into wedges and garnish with fresh cilantro.