Preheat oven to 400°F. Line a large rimmed baking sheet with parchment paper or a baking mat.
Slice the steak and vegetables. Slice the 1½ pounds sirloin steak thinly against the grain. Slice the 2-3 bell peppers and 1 large yellow or white onion.
Make the marinade. In a large bowl, combine 2 Tablespoons olive oil, 1 lime, juiced, 1 teaspoon chili powder, 1 teaspoon cumin, 1 teaspoon garlic powder, 1 teaspoon salt, and ½ teaspoon black pepper.
Toss everything together. Add the sliced steak, peppers, and onion to the bowl and toss until evenly coated. If time allows, let marinate for 20–30 minutes for extra flavor.
Spread onto sheet pan. Arrange the mixture in a single layer, making sure not to overcrowd the pan.
Bake for 15–20 minutes, or until the steak reaches your desired doneness and the vegetables are tender and slightly caramelized.
Serve immediately with tortillas and your favorite toppings.