Slice the flank steak into thin strips against the grain to ensure tenderness.
Slice the bell pepper and yellow onion into thin, uniform strips.
In a small bowl, combine the cumin, chili powder, sea salt, and black pepper to create a dry rub.
Toss the steak strips with half of the spice mixture until every piece is evenly coated.
Heat the avocado oil in a large skillet over medium-high heat until shimmering.
Add the steak to the skillet and sear for 2-3 minutes until browned and slightly charred; remove and set aside.
Add the peppers and onions to the same skillet, seasoning with the remaining spices, and sauté for 4 minutes until tender and caramelized.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle the shredded cheddar cheese over one half of the tortilla, then layer on the seared steak and sautéed vegetables.
Fold the tortilla in half and cook for 2 minutes per side until the cheese is melted and the exterior is golden and crisp.