Pat the sirloin steak dry with a paper towel and season both sides evenly with sea salt, black pepper, and garlic powder.
Heat 0.5 tsp of olive oil in a cast-iron skillet over medium-high heat until shimmering.
Place the steak in the skillet and sear for 3-4 minutes per side for medium-rare, then remove from the pan and let it rest for 5 minutes before slicing into thin strips.
In the same skillet, add the sliced red bell peppers and yellow onions, sautéing for 4-5 minutes until they are tender and slightly caramelized.
Wipe the skillet clean, add the remaining 0.5 tsp of olive oil, and place the tortilla in the pan over medium heat.
Sprinkle half of the shredded cheddar cheese onto one half of the tortilla, then layer the steak strips and sautéed vegetables on top.
Add the remaining cheese over the filling and fold the tortilla in half.
Cook for 2 minutes per side, pressing down gently with a spatula, until the tortilla is golden brown and the cheese is fully melted.
Slice into wedges and serve immediately.