Bring stock and mushrooms to boil in large saucepan. Boil 5 minutes. Remove from heat. Add bonito flakes, lemon grass, lime leaves, Korean red pepper and 1/2 teaspoon of the sea salt; let stand until bonito flakes sink to the bottom. Strain broth and reserve. Keep warm.
Blanch bok choy in large saucepan of boiling water until bok choy turns bright green and is lightly tender, about 1 minute. Drain immediately. Toss bok choy with sesame oil, Japanese Seasoning and remaining 1/4 teaspoon sea salt in large bowl.
To serve, ladle bonito broth into 6 serving bowls. Top each evenly with cooked noodles, seasoned bok choy and a poached egg. Garnish with radishes, cilantro, green onions and nori, if desired. Serve warm.