Thinly slice the sirloin steak against the grain into bite-sized strips and toss with sea salt, black pepper, garlic powder, and smoked paprika.
Heat avocado oil in a large non-stick skillet over medium-high heat until shimmering.
Add the steak strips to the skillet in a single layer and sear until deeply browned, about 2-3 minutes, then remove from the pan.
In the same skillet, add the sliced bell peppers and onions, sautéing for 3-4 minutes until tender-crisp and slightly caramelized.
Wipe the skillet clean and return to medium heat; place the tortilla in the pan and sprinkle half of the cheese over one side.
Layer the seared steak and sautéed vegetables over the cheese, then top with the remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side until the exterior is golden-brown and the cheese is fully melted.
Remove from the heat, let rest for 1 minute, then slice into wedges and serve immediately.