Heat the oil in a large saucepan and add the leeks and potato. Cook gently over a low heat whilst you chop the other vegetables. Stir often to stop them sticking to the bottom.
Add the garlic, courgette and stock. Simmer for 10-15 minutes until all the vegetables are tender.
Stir through the spinach until wilted and then blend with a stick blender. Season, and serve with a drizzle of olive oil and a sprinkle of dried chilli or sumac.