Soak mung beans for 2-3 hours in plenty of cold water.
Bring to a boil for 2 minutes, then drain.
Add the mung beans, onion, garlic, tomato, carrot, zucchini, celery, and 750 ml water or stock to a cooking pot and bring to a simmer. Season with salt and pepper.
Cook over medium-low heat for about an hour, or until the mung beans are tender.
Stir in the olive oil, lemon juice, and oregano.
Simmer for 10 minutes longer, stirring occasionally, until thick and creamy. If necessary, raise the heat slightly to help the soup thicken.
Serve drizzled with raw extra-virgin olive oil, and season with freshly ground pepper on top.