Stir tamarind and 3 tablespoon boiling water in a bowl until dissolved; pour through strainer into a food processor.
Puree the tamarind paste with sugar, oil, coriander, turmeric, salt, garlic, shallots, and ginger. Combine paste and lamb in a bowl and chill for 4 hours.
Build a hot charcoal fire in a grill. Thread 2 pieces of lamb each on 16 skewers and grill, turning, until lightly charred, about 4 minutes.