Cook noodles according to package directions. Cool, drain, and set aside.
In a small bowl, prepare wasabi according to package directions. Whisk the wasabi paste with the vinegar, garlic, and ginger. Slowly add the oil and continue whisking. Pour in the tamari and whisk again. Set aside.
Combine the spinach, red onion, tuna, and parsley in a large bowl, and fold in the cooked noodles. Pour the dressing over all, toss lightly and serve.