Combine lime juice and zest, cilantro, curry powder, and scallions in bowl and whisk.
Place steak in resealable bag and pour the marinade in bag to coat the steak. Let steak marinate for 30 to 45 minutes.
Heat a grill or grill pan to medium-high. Remove steak from marinade and place on grill. Season with salt and pepper.
Grill steak until browned, 8 to 10 minutes per side for medium-rare (cooking time depends on thickness of steak). Transfer steak to a cutting board and let rest 5 minutes before thinly slicing against the grain.