Preheat the Oven: Preheat your oven to 400°F (200°C).
Prepare the Marinade: In a large bowl, mix olive oil, lime juice, chili powder, cumin, garlic powder, salt, and black pepper. Add the sliced steak to the bowl and toss to coat evenly. Let it marinate for at least 15 minutes.
Arrange on Sheet Pan: Spread the marinated steak, bell peppers, and onion in a single layer on a large sheet pan.
Bake: Roast in the preheated oven for 20-25 minutes, or until the steak is cooked to your liking and the vegetables are tender and slightly charred.
Serve: Remove from the oven and serve the fajitas with warm tortillas and your choice of toppings.