Bring a small pot of water to a boil, gently lower the egg in, and cook for 6.5 minutes before transferring immediately to an ice bath.
Cook the soba noodles in boiling water according to package directions, then drain and set aside.
Season the chicken breast with sea salt and black pepper, then sear in a hot pan with half of the sesame oil until golden and cooked through.
In a separate pot, sauté the grated ginger, minced garlic, and sliced shiitake mushrooms in the remaining sesame oil until fragrant.
Pour in the chicken bone broth and tamari, bringing the liquid to a light simmer.
Add the chopped baby bok choy to the broth and cook for 1 minute until just wilted.
Assemble the bowl by placing the noodles at the bottom, pouring over the hot broth and vegetables, and topping with the sliced chicken.
Peel and halve the soft-boiled egg, placing it on top of the ramen, and garnish with sliced green onions.