Method:
In a large pot, bring broth to a boil. Submerge noodles in broth, arranging them across the bottom of the pot, cover and simmer until noodles are somewhat tender, 4 to 5 minutes. Scatter shrimp and broccoli over noodles, cover and simmer until shrimp are just cooked through, broccoli is bright green and noodles are tender, 4 to 5 minutes more. Meanwhile, whisk together water, miso and ginger in a medium bowl until smooth; set aside.
Turn off heat and uncover pot. Stir in miso mixture and green onions then transfer soup to bowls. Garnish with pepper flakes and serve.