In a skillet, heat 1 tablespoon vegetable oil. Add 4 thinly sliced garlic cloves and cook over moderately low heat, stirring a few times, until golden brown, about 1 minute.
Add 1 teaspoon sugar and cook for about 20 seconds. Add 1 pound ground pork or beef and cook over moderately high heat, breaking up the meat in the skillet, until no pink remains, about 3 minutes.
Add 1 teaspoon fish sauce and season with salt and pepper.
In a medium skillet, cook 1 tablespoon long-grain rice over moderate heat, shaking the pan, until browned, about 3 minutes. Transfer the rice to a spice grinder and let cool, then grind to a powder.
In a small bowl, combine 2 tablespoons fresh lime juice with 2 tablespoons fish sauce, 1 tablespoon sugar, 2 thinly sliced Thai chilies and 1 tablespoon water. Stir well until the sugar dissolves.
Repeat the pork. Off the heat, stir in 1 thinly sliced Thai chile, one-quarter thinly sliced red onion and ½ cup each of torn basil, mint and cilantro leaves. Sprinkle the pork with the rice powder, spoon into Boston lettuce leaves and serve with the sauce.