Heat a dash of oil in a large frying pan over a medium-high heat. Halve the leek lengthwise, slice it thinly, and add it to the pan. Dice the pepper and mushrooms, and add those too. Cook for a few minutes, stirring regularly, until the vegetables are fairly soft.
Add the chickpeas, tomatoes, tomato puree and curry powder, and mix well. Turn the heat up high, and bring to a simmer. Season to taste, and allow to cook for another 5 minutes, or until the sauce has thickened to your desired consistency.
Add the cream if using, and serve topped with fresh coriander.