Bring a small pot of water to a boil and cook the egg for 7 minutes for a jammy yolk, then transfer to an ice bath, peel, and set aside.
In the same pot, cook the soba noodles according to package directions, drain, and rinse with cold water to prevent sticking.
Season the pork tenderloin with sea salt and black pepper, then sear in a pot with toasted sesame oil over medium-high heat until browned and cooked through.
Remove the pork to rest, then in the same pot, sauté the minced garlic, grated ginger, and sliced shiitake mushrooms until aromatic and softened.
Pour in the chicken broth, tamari, rice vinegar, and sriracha, bringing the liquid to a gentle simmer.
Add the baby bok choy to the broth for 2 minutes until just wilted and bright green.
Slice the pork thinly and divide the noodles between bowls.
Ladle the hot spicy broth and vegetables over the noodles, then top with the halved egg and sliced green onions.