In a medium pot, bring the chicken broth, minced garlic, grated ginger, and tamari to a gentle simmer over medium heat.
Submerge the chicken breast in the liquid and poach for 12 minutes until the center is opaque, then remove and shred using two forks.
Cook the soba noodles in a separate pot of boiling water until al dente, then drain and rinse under cold water to prevent sticking.
Add the bok choy and sliced mushrooms to the aromatic broth, simmering for 3 minutes until the greens are bright and tender.
Whisk in the sriracha, sesame oil, sea salt, and black pepper to create a silky and spicy finish to the soup base.
Place the cooked noodles in a deep bowl, pile the shredded chicken and vegetables on top, and ladle the hot broth over the dish.