Peel the onions and finely slice them. Peel the garlic and crush or finely chop. Trim the roots and top 3cm off the leeks. Slice the leeks in half lengthways. Rinse out any dirt. Finely slice them.
Fill a pan with water. Sprinkle in a good pinch of salt, cover and bring to the boil.
While the water heats, drizzle 1 tbsp oil into a large pan and warm to a medium heat. Slide in the chopped onions, leeks and garlic. Sprinkle in 1 tbsp ground cumin and 1 tsp turmeric, along with a pinch of salt and pepper. Fry for 10 mins, stirring occasionally, till softened.
Crumble the stock cube into the pan with the leeks. Drain and rinse the chickpeas, then tip them into the pan. Pour in 700ml boiling water and stir well. Bring to the boil, then reduce the temperature to low. Simmer for 10 mins.
While the leek and chickpea broth cooks, tip the spaghetti into the pan with the boiling water. Cook for 8-10 mins, or till tender with a little bite. Drain well.
When the broth is ready, stir through the baby leaf spinach till the leaves are wilted. Squeeze in the juice from half the lime.
Pile the drained spaghetti into deep bowls and ladle over the leek and chickpea broth. Dollop over generous spoonfuls of yogurt. Finely chop the parsley and sprinkle over the top. Serve with wedges of the remaining lime for squeezing.