Thinly slice the top sirloin steak against the grain into bite-sized strips.
In a small bowl, combine the sea salt, black pepper, garlic powder, and smoked paprika, then toss with the steak strips to coat evenly.
Heat the avocado oil in a large skillet over medium-high heat.
Add the sliced 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 pan and add the steak strips in a single layer, searing for 2 minutes per side until browned and cooked through.
Remove the steak and vegetable mixture from the pan and wipe the skillet clean.
Place the whole wheat tortilla in the skillet over medium heat, sprinkling the shredded cheddar cheese over one half.
Top the cheese with the steak and pepper mixture, then fold the tortilla in half.
Cook for 2 minutes per side until the tortilla is golden brown and the cheese has fully melted.
Slice into wedges and serve immediately.