Make the sauce. In a medium-sized mixing bowl, whisk the peanut butter with the lime juice, Mirin, soy sauce, sugar, chili paste and 2 tablespoons of the grapeseed oil. Set aside.
Cook onion and garlic. Coat a large sauté pan or wok with the remaining tablespoon of grapeseed oil. Place the pan over low-medium heat and add the onion and garlic. Sauté until the onion is soft, about 7 minutes and slightly golden.
Add remaining vegetables and cook. Turn the heat up to medium-high and add the carrots, bean sprouts, peppers and cabbage. Stirring occasionally, cook until the carrots are tender, about 7 minutes. Remove the pan from the heat and set aside.
Cook the noodles. Cook the noodles in a large pot of boiling, salted water just until tender but still firm to bite, about 6 minutes. Before draining, remove ½ cup of the noodle water and add it to the vegetable mixture. Then drain the noodles and add them, too.
Add fresh herbs, sauce and garnish to the noodles. Add the cilantro, mint, scallions, and pour the sauce over the entire mixture. Gently toss to evenly combine all of the ingredients and season to taste with salt and pepper (if necessary), and Garnish with the peanuts.