To make the sauce: In a large bowl, mix together all the sauce ingredients until well blended. Set aside. To make the noodle salad: Bring a large pot of water to a boil, cook the udon noodles for 8 to 10 minutes. Drain and rinse under cold water. Add all the vegetables and noodles into the large bowl with the peanut butter sauce. Stir until well coated. Season with more soy sauce, vinegar, sesame oil and chili garlic sauce if needed. It can be served right away. Divide the noodles among the serving plates, and sprinkle some peanuts on top. The noodle salad can be made one day ahead, and keep it in the refrigerator for overnight to allow the flavor to marry.