Cook the pasta in a large pot of water according to the directions on the package. Drain and rinse with cold water. While the pasta is cooking put the broccoli in a steamer basket over a large pot of boiling water and steam it for 3 minutes. 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 until they become fragrant, about 3 minutes. Set them aside to cool. 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.
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. Drizzle the remaining sauce over the vegetables. Coarsely chop the peanuts, sprinkle them on top and serve.