Heat neutral oil over medium-high in a large soup pot. If using mushrooms, sautée for several minutes until cooked. Remove mushrooms and set aside.
Add another drizzle of oil if necessary. Add onion and cook till translucent. Add garlic and ginger and cook for a few more minutes.
Add stock, kimchi and kimchi juice to the pot. Mix the miso in a small bowl with a ladleful of stock, then add it to the pot with the soy sauce, then bring to a simmer. Season to taste with salt.
Add noodle blocks, then cover the pot and cook for a few minutes. When the noodles are tender, stir to break them up and remove the pot from the heat.
Ladle the soup into bowls and garnish with toppings. Serve immediately.