While noodles are soaking, stir together the peanut butter, brown sugar, soy sauce, ginger, chili paste, and garlic in a medium bowl. The mixture will be thick. Add some water a little at a time until it reaches the desired consistency - not too thick, but thin enough to coat the noodles. Usually 1/4 to 1/2 cup is all that is needed. (The flavor will be strong, but will be diluted when tossed with the noodles and veggies.)