Put 2 tsp coriander seeds in a dry pan. Set over a medium heat and toast for 2 mins till the seeds smell aromatic. Tip into a mortar and pestle or spice grinder and crush. No grinder? Put them in a small bowl and use a rolling pin or jam jar to crush them. Set aside.
Peel and finely chop the onion. Peel and crush the garlic. Drain and rinse the chickpeas.
Put the pan back on the heat and warm for 1 min. Add the onion with 1 tbsp oil and a pinch of salt and pepper. Cook and stir over a medium heat for 8 mins till the onions have softened and start to brown.
Stir in the garlic and crushed coriander seeds. Add the chickpeas and dried lentils and give everything a stir.
Tip in the tomatoes. Pour in 800ml boiling water. Cover, bring to the boil, then reduce the heat and simmer for 15 mins.
While the soup simmers, break the spaghetti into little lengths, around 2cm long. After 15 mins, add to the pan. Put the lid back on and simmer for 8 mins till the spaghetti and lentils are tender.
Squeeze the juice from half the lemon into the pan and give it a good stir. Taste and add more salt and pepper or lemon juice if you think it needs it. Serve in warm bowls.