Slice the flank steak into thin strips against the grain to ensure tenderness.
Season the steak strips evenly with sea salt, black pepper, garlic powder, and cumin.
Heat the avocado oil in a large skillet over medium-high heat until shimmering.
Add the sliced red bell pepper and red onion to the skillet, sautéing until they are slightly softened and charred.
Push the vegetables to the side of the pan and add the steak strips, searing for 2-3 minutes until browned and cooked through.
Remove the steak and vegetables from the pan and wipe the skillet clean with a paper towel.
Place the whole wheat tortilla in the skillet, sprinkling half of the shredded cheddar cheese over one side.
Layer the seared steak and vegetable mixture over the cheese, then top with the remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is golden-brown and the cheese is completely melted.