To prepare the radishes, place the radish slices in a mason jar big enough to hold them. Whisk together the boiling water, vinegar, salt, and sugar. Pour this mixture over the radishes. Cover and allow them to sit for at least 20 minutes before using. The radishes will keep in an airtight container for several weeks in the fridge.
To make the sauce, place all ingredients in a small bowl and whisk together. Start with two tablespoons warm water and add another if the sauce is too thick for your liking. The sauce will keep in an airtight container in the fridge for up to five days, and it can be prepared ahead of time, along with the radishes.
To make the bowls, bring a large pot of water to boil. Add the dumplings gently, a few at a time. Boil for one minute, then reduce the heat to low. Simmer for 2 more minutes, than use a slotted spoon to remove them from the water.
Divide the veggies and radishes between four bowls, then add 5 cooked dumplings to each bowl. Top each bowl with a couple tablespoons of sauce and a garnish of green onion tops, if you like. Serve.