Add the noodles to a large pot of boiling water,and cook until tender. Strain the noodles, shock in a bowl of ice water, and drain. Using kitchen scissors, cut the noodles into bite-size pieces, then transfer to a large bowl. Toss with 1 tsp. of sesame oil.
Season the vegetables with salt and lots of black pepper. Heat the grapeseed oil in a large pan. Add the onions and peppers and cook until the onions become soft, about 8 to 10 minutes.
Add the carrots, mushrooms, green onions, and garlic and cook another 10 minutes.
Deglaze the pan with mirin, and add the vegetables to the noodles. Stir in the soy, vinegar, toasted sesame oil, and seeds, and season to taste with salt and pepper.
Mix the noodles and vegetables together. Serve at room temperature or cold.