In medium mixing bowl, blend garlic, olive oil, mint, and lime zest and juice. Add lamb sirloin steaks to marinade in a glass baking pan for at least 2 hours, covered (ideally, overnight).
Preheat grill. Meanwhile, remove lamb from marinade. Lightly score sirloins, approximately 4 cuts per side. Place on grill over low heat. Cook for approximately 4 minutes per side.