Bring a large pot of water to a boil. Add the soba noodles and cook until the noodles are cooked through, 2 to 3 minutes. Strain through a medium mesh sieve and rinse the noodles under cold running water for 1 minute.
Meanwhile, make the broth. Bring the chicken broth, soy sauce, garlic, and ginger to a boil in a large saucepan over high heat. Reduce the heat to medium and simmer for 3 minutes, then add the mushrooms and simmer until they’re tender, about 5 minutes. Add 3/4 of the scallions and simmer until soft, about 1 minute.
Divide the noodles among 4 bowls and pour the soup over the noodles. Add the spinach or greens, sprinkle with the remaining scallions and serve each bowl with a hard boiled egg half. Kampai!
Did you Know!? If you’re gluten intolerant or are making soba noodles for someone who is, be sure to read the ingredient list on the package. Sometimes wheat flour is mixed in with buckwheat flour, so read away!