Slice the flank steak into thin strips against the grain for maximum tenderness.
In a small bowl, toss the steak strips with chili powder, cumin, garlic powder, sea salt, and black pepper until evenly coated.
Heat the avocado oil in a large skillet over medium-high heat until shimmering.
Add the bell peppers and red onion to the skillet, sautéing for 3-4 minutes until they are tender-crisp and slightly charred.
Push the vegetables to the side of the skillet and add the seasoned steak, searing for 2 minutes per side until browned and cooked through.
Squeeze the juice from the lime over the steak and vegetable mixture, tossing to combine, then remove everything from the pan.
Wipe the skillet clean and place the tortilla in the pan over medium heat.
Sprinkle half of the cheddar cheese on one side of the tortilla, top with the steak and pepper mixture, and add the remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is golden and the cheese is fully melted.