Fire up a rotisserie, using charcoal as the heat source. (Medium-high heat for this dish is advised.) If necessary, tie the lamb with kitchen string. Push the spit through roast - length-wise. Secure it to the spit with the provided skewers. Position the spit on the rotisserie. Turn the motor on, allowing the the lamb to rotate until it is medium-rare, about 45 minutes. Remove the spit from the rotisserie, salt the lamb down and rest it - tented under aluminium foil - for 10 minutes. Remove the spit and carve the lamb against the grain into thin wafter-thin slices. Stuff them into pitas with sliced tomatoes, purple onions and tzatziki.