Slice the top sirloin into very thin strips against the grain to ensure a tender bite.
Toss the steak strips in a small bowl with the sea salt, black pepper, garlic powder, and cumin until evenly coated.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until the oil is shimmering.
Add the steak to the hot skillet in a single layer and sear for 2 minutes to develop a deep brown crust, then flip and cook for 1 minute more.
Remove the steak from the skillet and add the sliced red peppers, green peppers, and onions, sautéing for 4 minutes until they are softened and slightly charred.
Wipe the skillet clean and place the whole wheat tortilla inside over medium heat.
Sprinkle half of the shredded cheddar over one half of the tortilla, then layer on the cooked steak and sautéed vegetables.
Top with the remaining cheese and fold the tortilla in half, pressing down firmly with a spatula.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese has completely melted into the filling.
Slice into wedges and serve immediately while the exterior remains perfectly crisp.