In a medium skillet, toast the rice over moderate heat, shaking the pan often, until browned, about 3 minutes. Transfer the rice to a plate and let cool completely. Put the toasted rice in a spice grinder and grind to a powder.

In the skillet, heat the oil. Add the garlic and cook over moderately low heat, stirring a few times, until golden brown, about 1 minute. Add 1 teaspoon of the sugar and cook for about 20 seconds. Add the ground pork and cook over moderately high heat, breaking up the meat finely, until no pink remains, about 3 minutes. Add 1 teaspoon of the fish sauce and season with salt and pepper. Set aside.

In a small bowl, combine the lime juice with the remaining 2 tablespoons of fish sauce, the remaining 1 tablespoon of sugar, two-thirds of the chiles, and 1 tablespoon of water. Stir to dissolve the sugar.

Arrange the lettuce leaves on a platter with the dipping sauce. Reheat the pork. Remove from the heat and stir in the onion, basil, mint, cilantro, and the remaining chile. Sprinkle the pork with the rice powder. Transfer to a bowl and place on or near the platter. Let everyone spoon the pork onto the lettuce leaves and season with the dipping sauce.