Slice the flank steak into thin, bite-sized strips across the grain.
In a small bowl, toss the steak strips with lime juice, chili powder, cumin, sea salt, and black pepper until evenly coated.
Heat half of the avocado oil in a large skillet over medium-high heat.
Add the sliced bell peppers and red onions to the skillet, sautéing for 3-4 minutes until tender and slightly charred, then remove from the pan.
Add the remaining avocado oil to the same skillet and sear the steak strips for 2 minutes per side until browned and cooked through.
Wipe the skillet clean and place the whole wheat tortilla in the pan over medium heat.
Sprinkle half of the cheddar cheese on one side of the tortilla, then layer on the cooked steak, peppers, and onions.
Top with the remaining cheese and fold the tortilla in half.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately.