Sirloin steak is recommended for this recipe because it is leaner meat that is really suitable for grilling. It will not cause the grill to flame as excess fat drips off it, and the meat and vegetables will not burn. Sirloin also holds its form on a skewer during the cooking process.  Roast and beef stew meat isn’t a good choice for these steak fajitas skewers as the meat is quite tough.