Preheat the oven to 475°F and line a baking sheet with parchment paper or lightly oil it.
On the prepared sheet pan, place the steak and sliced onion. Sprinkle garlic powder, chili powder, chipotle chili powder, smoked paprika, cumin, dried oregano, salt, and the olive oil over the steak and onion; toss or rub to coat evenly.
Arrange the corn kernels around the meat in a single layer.
Bake at 475°F for 10 minutes, then switch the oven to broil and broil 2–5 minutes until the edges of the steak begin to crisp; watch closely to avoid burning.
Remove the sheet pan and let the steak rest 10 minutes, then thinly slice against the grain and toss the slices with the roasted corn.
Make the sauce by whisking together the salted butter, chopped chipotle chile, hot sauce, lime juice, and seasoned salt in a bowl until combined.
Spoon the sauce lightly over the sliced steak and corn, then fill warmed tortillas with the steak mixture and top with avocado, feta, cilantro, and extra sauce as desired.