Make the ramen: Bring a small pot of water to a boil. Add the ramen, lower the heat to medium-high, and cook for about 4 minutes, until the noodles are soft and easy to separate with a fork. Drain the ramen in a colander and rinse to remove excess starch.
While the ramen is cooking, heat a Dutch oven or a large pot over medium-high heat. Add a splash of the vegetable broth and the onions and cook for about 6 to 8 minutes, until softened. Add another splash of broth at any point if needed to prevent sticking.
Add the carrots, celery, and ginger to the pot and cook for about 6 minutes, or until the carrots and celery have softened.
Add the garlic, Italian seasoning, pepper, and turmeric to the pot. Stir well and cook for about 1 minute.
Add the rest of the broth to the pot and bring to a boil. Once boiling, reduce the heat to medium-low and continue to simmer for about 15 minutes.
After the soup has simmered for about 15 minutes, remove it from the heat. Carefully ladle out about a cup of the broth into a small bowl. Add the miso to the bowl, whisk to break up any chunks and combine, and return the miso-broth mixture to the pot.
Add the spinach to the pot and stir until just wilted. Then, add the ramen, freshly squeezed lemon juice (start by adding 1 tablespoon and tasting, then adding additional lemon juice to taste if desired), and basil leaves (if using). Stir well and serve immediately.