To prepare the dressing, combine the fish sauce, lime juice, 2 tablespoons of the brown sugar, 6 tablespoons of the water, the garlic and the chile. Whisk well. Taste: if it's too pungent, add more water, 1 tablespoon at a time. If you'd like more sweetness, add more brown sugar, 1/2 tablespoon at a time. Remember that you're going to be putting this dressing on unsalted vegetables and noodles: you want the dressing to have a lot of flavor, but it shouldn't knock you over. Pour into a serving bowl. (Covered and chilled, the dressing will keep for 3 days to a week.).
Bring a large pot of water to a boil. Add the rice noodles, and cook for 4 to 5 minutes, until tender but not mushy. Immediately drain the noodles into a colander, and rinse them well with cold water. Lay out a clean kitchen towel on the countertop, shake the colander to drain away excess water and then spread the cooked noodles on the towel to drain further.
Divide the noodles between two or three good-sized bowls, depending on the number of diners, and top with the vegetables, herbs and meat. Scatter the peanuts on top. Allow each person to spoon on dressing to taste. Toss well, and eat. (Alternatively, you can present this salad family-style: Toss the vegetables, herbs and noodles in a mixing bowl and then mound them on a serving platter. Arrange the meat over the noodles, and top with peanuts. Each diner can scoop their own portion from the platter and dress it as they see fit.).