Lay the flank steak in the middle of a baking sheet. Arrange the bell peppers and red onion around it. Drizzle everything with olive oil and season with salt, pepper, chili powder, garlic powder, and cumin.
Using your hands, rub the seasoning into the vegetables, then into the steak. Flip the steak and season the other side.
Squeeze the lime juice over the top of the steak and veggies.
Cook for 12 minutes, or until the meat has reached your desired doneness.
Transfer the steak to a cutting board and let it rest for 10 minutes, then slice it into pieces, going against the grain.
Fill up a warm tortilla with the steak, bell peppers, and onion.