Thinly slice the flank steak against the grain into bite-sized strips to ensure a tender texture.
In a medium bowl, toss the steak strips with lime juice, chili powder, cumin, sea salt, and black pepper until thoroughly coated.
Heat the avocado oil in a large non-stick skillet over medium-high heat until shimmering.
Add the bell peppers and red onions to the skillet, sautéing for 3-4 minutes until they are softened and slightly charred.
Push the vegetables to the edges of the pan and add the steak strips to the center, searing for 2-3 minutes until browned and caramelized.
Remove the steak and vegetable mixture from the pan and set aside, then wipe the skillet clean with a paper towel.
Place the whole wheat tortilla in the skillet over medium heat and sprinkle the sharp cheddar cheese evenly over one half.
Layer the cooked steak and vegetable mixture over the cheese and fold the tortilla in half.
Press down firmly with a spatula and cook for 2 minutes per side until the tortilla is golden brown and the cheese is fully melted.
Transfer to a cutting board, slice into three wedges, and serve immediately while hot.