Start by chopping the onion into very small pieces. Set aside.
Also cut the zucchini into cubes and the leek into rounds. Set aside.
Put the chopped onion in a pot with olive oil and cook over medium-high heat for 2 min or until it starts to get soft.
Add the zucchini and leek and cook for another 1 or 2 min.
While the vegetables are cooking, you can boil the water in a kettle (I find it easier this way because the noodles only need to be slightly boiled, but you can boil water in a pot for example).
Add the miso paste to the pot of vegetables and let it dissolve slightly.
If you want to add the vegetable broth, put it in the pot now and let it boil.
Add the boiling water and let the rest of the miso paste dissolve.
Season with salt and pepper and add the spinach and soba noodles.
Cook for about 3 minutes and turn off the heat. Let it rest.
Meanwhile, boil the eggs for 6 min (so that they are undercooked) or, 7 to 10 min, if you prefer hard-boiled eggs.
Add the soy sauce to the broth, if you choose to add it.
Assemble your vegetarian ramen: place the noodles in a bowl, then the broth and the vegetables.
Add an egg broken in half and some nori or wakame seaweed.
Repeat the assembly process for the second bowl.
You can also add some sesame seeds on top.