Thinly slice the top sirloin steak against the grain into bite-sized strips.
In a small bowl, combine the sea salt, black pepper, cumin, and garlic powder, then toss the steak strips in the seasoning until evenly coated.
Heat the avocado oil in a large cast-iron skillet over medium-high heat.
Add the sliced bell peppers and red onions to the skillet, sautéing for 3-4 minutes until they are softened and have developed a slight char.
Push the vegetables to the side of the pan and add the steak strips in a single layer, searing for 2 minutes per side until browned and cooked to your preference.
Remove the steak and vegetable mixture from the skillet and set aside.
Wipe the skillet clean and place the whole wheat tortilla in the center.
Sprinkle the shredded sharp cheddar cheese over one half of the tortilla, then top with the steak and pepper mixture.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately while hot.