To make homemade miso soup, take a large pot and heat oil in it over medium heat. Before adding all the vegetables, mushrooms and tofu, as mentioned above, add ginger, garlic, and onions. Cook them on medium heat until they turn translucent. This should ideally not take over 5 minutes.

Thereafter, add the vegetable broth, chopped vegetables, and the tofu and bring them to a boil.  Reduce the heat and simmer the vegetables until they become tender. This should not take more than 5-10 minutes. Once done, remove the soup from the heat. Add salt and pepper as per taste. 

Now in a small bowl, serve about one cup of the hot broth. Add red miso, cayenne pepper (optional) and stir till it is properly mixed. Remember, cayenne pepper is added to just make the soup spicier so exercise caution on how much or whether you want to add it. Thereafter, transfer it into a pot and keep stirring. Add vinegar while you stir and ladle it into bowls and garnish them with green onions.