How to Make It
In a bowl, combine the ground beef with all the remaining ingredients except the grape leaves. Cover with plastic wrap and refrigerate for at least 4 hours or overnight.
Snip off any stems from the grape leaves. Spread 4 leaves on a work surface. Form a 1-tablespoon-size log of the beef filling at the stem end of each leaf. Fold the sides of each leaf over the filling, then tightly roll up the leaves to form 4 cylinders. Repeat with the remaining grape leaves and filling.
In a bowl, whisk the sugar into the hot water until dissolved. Whisk in the remaining ingredients, except the garnishes. Transfer the nuoc cham to a serving bowl.
Light a grill. Lightly brush the grill and beef rolls with oil. Arrange the rolls on the grill and cook over moderate heat, turning often to prevent burning, until firm and just cooked through, about 8 minutes. Sprinkle the rolls with cilantro and mint. Serve warm with lettuce leaves for wrapping and the nuoc cham for dipping.