1. Cook the pasta according to the directions on the package. Drain and rinse with cold water. While the pasta is cooking, steam broccoli in a steamer for 3 minutes.
2. Add the snow peas and sugar snap peas and steam for 2 minutes more. Toast the peanuts in a dry pan over a medium heat, about 3 minutes, if desired. Set them aside to cool.
3. Make the sauce by pureeing the peanut butter, soy sauce, water, vinegar, lime juice, scallion, ginger, sugar and red pepper flakes in a food processor or blender until smooth.
4. Right before serving, toss the pasta with 3/4 cup of the peanut sauce. Divide into 6 serving bowls and top each serving with the vegetables.
5. Drizzle the remaining sauce over the vegetables. Coarsely chop the peanuts, sprinkle them on top and serve.