In a large pot or Dutch oven, heat the olive oil over medium heat.
Add the garlic, ginger, and onions and sauté until onions become translucent.
Add vegetable stock, water, shiitake mushrooms, and soy sauce.
Stir and simmer for at least 45 minutes, up to 3 hours.
The longer you simmer, the more flavorful the broth will become.
Uncover the pot, add the miso paste, and stir.
Ladle the broth into a bowl and add noodles and toppings of your choice.