1. Place the lentils in a sieve and rinse them under cold running water until the water runs clear.
2. Heat a large pot over medium heat with olive oil.
3. Add diced onion to the pot and cook for 3–4 minutes, stirring occasionally, until it softens and becomes slightly translucent.
4. Add the garlic and cook for another 1–2 minutes until fragrant.
5. Add carrot and celery and cook for around 3 minutes to soften slightly.
6. Add the oregano, rosemary and tomato paste and stir, cooking for 1 minute.
7. Add in the rinsed lentils, bay leaves and 1 litre of water to start. Stir everything together.
8. Bring the pot to a gentle boil, then reduce the heat to low. Cover the pot with a lid and let the soup simmer for 30–40 minutes, stirring occasionally.
9. Check the consistency, if it looks too thick, add more water (up to another ½ litre). If the lentils aren’t soft yet, continue cooking until they are tender.
10. Ladle the soup into bowls.