Bring 6 cups of stock and the ginger to a boil in a large pot over high heat.
While water is heating, sear the tofu or chicken – heat oil over medium high heat, in a skillet. When oil is hot, add a generous 4 finger pinch of salt and pepper to the oil. Give a stir. The pepper will smell fragrant. Carefully add the tofu (or chicken), to the hot oil, letting it get golden brown, turning gently with a metal spatula, until golden. You may need to turn the heat down to med. (This simple preparation really enhances the texture and flavor, but to lower the fat, you could add tofu to the soup, without searing it.) Once tofu is brown, blot and set aside. (You can brown the mushrooms the same way, or add them directly to the broth.)
Once stock comes to a simmer, add hondashi and miso, and stir until dissolved. Add kale, mushrooms, vegetables and soba noodles, keeping at a low simmer, with pot uncovered. Stir occasionally. Soba noodles will be cooked in 4-5 minutes and veggies lightly wilted.
Add scallions, and a little squirt of Sriracha, or more to taste. Add a teaspoon of toasted sesame oil. Now taste for salt. If you don’t use the sriracha sauce, you may need just a little squeeze of lemon or lime juice.