Measure out 2 tsp cumin seeds. Add to a dry pan and toast over a medium heat for 2 mins till they pop and smell nutty. Tip into a bowl and set aside. Take the pan off the heat.
Peel and finely chop the onion and carrot. Trim the ends off the celery stick. Finely chop it. Halve the pepper and scoop out the seeds and white bits. Finely chop it.
Put the pan back on the heat for 1 min. Add ½ tbsp oil and the chopped veg. Season. Cover and sweat over a medium heat for 8 mins till they start to soften.
Meanwhile, peel and crush or grate the garlic. Stir the garlic into the veg with ¾ of the cumin seeds and the bay leaf. Crumble in the stock cube. Stir in the red lentils. Pour in 800 ml boiling water (or use hot homemade stock). Cover, turn the heat up and bring to the boil.
Turn the heat down and simmer for 15- 20 mins till the lentils are tender. Fish out the bay leaf. Taste the soup and season. Ladle into warm bowls and sprinkle with the last of the cumin seeds to serve.