Put lentils in a medium sized pot with the vegetable stock and bay leaf.
Bring to a boil for 10 minutes, then reduce to a simmer, cover with a lid, and cook for another 20 minutes.
Add the garlic, onions, oregano, pepper, and turmeric and simmer for another 5 minutes, or until the lentils are tender. Once tender, add salt to flavour.
Turn off the heat, stir in the mizuna leaves, cover, and let the soup stand for 10 minutes to wilt the mizuna and to absorb the seasonings.