Start by splitting the lobsters in half lengthwise: using a sharp knife, slice from the tip of the head, straight through the body and the tail. Clean the lobster thoroughly, removing the stomach and soft green tomalley (liver).
In a mortar and pestle, put in whole garlic clove and two chilies, and pound until they are blended.
Add sugar, fish sauce, and lime juice. Mix hot sauce together using a whisk.
Place lobster halves on a hot grill directly over the flame, shell side down. When the meat starts to turn opaque, brush it with the hot sauce, and then then turn over to cook the meat until fully opaque and showing grill marks.
The sauce is spicy, so use your discretion and be sure to savor every last drop of this delicious sauce!