Cook your noodles according to the package instructions. Drain, rinse with cold water, and set aside.
Add 1 cup water, miso, white parts of the scallions, ginger, garlic, and cilantro stems to blender and blend on high until totally smooth.
In a medium to large pot over medium heat, add the miso mixture and simmer for about 1 minute, stirring constantly.
Stir in the remaining 7 cups water and soy sauce. Add the tofu and veggies, then cover and increase the heat to high to bring to a boil. Give it a stir, then reduce the heat to low and simmer, covered, for 10 minutes, or until the veggies are just tender.
Stir in the lemon juice. Taste and add more salt or soy sauce, if needed. Add noodles to a soup bowl and ladle the soup over top. Top with fresh herbs, a soft-boiled egg (if using), and sriracha (if using).