Prepare the soba noodles according to the directions. Toss with a little oil and set aside.[br]
Heat the vegetable oil in a large sauté pan over medium-high heat. Add the shrimp (if using) and cook until lightly browned – about 2 minutes on each side. Remove from pan and set aside.
Add the onion, garlic, 1 tablespoon ginger, bok choy stems, and carrots to the pan. Cook, stirring constantly, until vegetables are just softened – about 7 minutes.[br]
Add the cooked noodles, shrimp, boy choy greens and mushrooms to the pan. Stir together the ponzu, lime juice, sambal oelek, and remaining ginger. Pour the sauce over the noodles. [br]Continue to cook, stirring constantly, until the shrimp are done – about 10 minutes. Remove from heat and stir in the basil.