To streamline the preparation, cook the noodles ahead of time, and have the vegetables already marinating in a bag. Another quick tip: Remove the potato slices from the simmering water using a slotted spoon, then return the water to a boil, and use the same pot to cook the soba. Use a spatula to carefully turn the potatoes on the grill so they won't stick.
Place potato slices in a saucepan, and cover with water; bring to a boil. Reduce heat, and simmer for 5 minutes or until crisp-tender; drain. Rinse with cold water; drain well.
Combine juice and the next 5 ingredients (juice through garlic) in a large zip-top plastic bag. Add potato slices, eggplant, and bell pepper to bag; seal and marinate in refrigerator for 1 hour, turning bag occasionally. Remove the vegetables from bag, reserving marinade.
Place the vegetables on grill rack coated with cooking spray, and grill for 4 minutes on each side or until done, basting frequently with 1/2 cup reserved marinade. Place vegetables on a platter; drizzle with remaining marinade.
Combine onions and next 5 ingredients (onions through ginger). Place soba in a large bowl, and drizzle with dressing. Serve with vegetables.