In a large soup pot or Dutch oven, sauté garlic and ginger in olive oil for 2-3 minutes just until fragrant
Add water, soy sauce and mushrooms and bring to the boil.
Turn heat to simmer then add the noodles and carrot. Cook for another 2-3 minutes just until the buckwheat noodles soften. Remove from heat.
In a small bowl, whisk white miso paste into a splash of warm broth until it forms a perfectly smooth liquid. Stir it into the soup together with the spinach then transfer soup to two large bowls. Add your toppings of choice and serve.