Heat the oil in a stock pot over medium heat. Add the shallots, garlic, ginger and serrano. Cook down for a couple of minutes. Add the cabbage and toss to combine. Pour in the water, soy sauce and rice vinegar. Spoon in the miso. Bring to a boil, lower the heat and simmer for 10-15 minutes, or until the cabbage is tender.
Meanwhile, bring a pot of water to a boil and cook the soba noodles according to the package instructions. Drain and rinse with cold water.
To the soup, add the herbs, lime juice, sriracha and pepper. Taste the broth and adjust the seasonings as needed - add more soy sauce, sriracha, lime juice, vinegar or herbs. Don't be afraid to play around until you love it!
To serve, add noodles to each bowl and top with the soup. Serve with extra lime wedges, more herbs and a drizzle of sesame oil.