Add all of the ingredients to a slow cooker. (Optional: You can saute the onions in a little olive oil before adding them.) Cook at a low temperature for 6 to 12 hours (until sauce reduces and thickens). A small amount of habanero pepper (chopped or sauce), can be added for additional heat, to taste, at the end of cooking. Serve warm with pork BBQ and white bread or hamburger buns.;
Note: Key ingredients are the fresh ginger, allspice, peppers, and tamarind. Also, the flavor is better (and a little milder) if it cooks longer.