Thinly slice the sirloin steak against the grain and season with sea salt, black pepper, garlic powder, and smoked paprika.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the steak to the skillet in a single layer and sear for 2-3 minutes until a golden-brown crust forms, then remove and set aside.
In the same skillet, add the sliced bell peppers and onions, sautéing for 4-5 minutes until they are tender and slightly charred.
Wipe the skillet clean and place the whole wheat tortilla inside over medium heat.
Layer the shredded cheddar, seared steak, and sautéed vegetables over one half of the tortilla.
Fold the tortilla in half and cook for 2 minutes per side, pressing down gently, until the cheese is melted and the exterior is toasted.
Transfer to a cutting board, let rest for one minute, and slice into three wedges before serving.