Spicy lentil & tomato soup

1 tablespoon vegetable oil

1 large onion, finely chopped

2 garlic cloves, finely chopped

1 small green chilli, deseeded and finely chopped

250 g (8 oz) red lentils, washed and drained

1 bay leaf

3 celery sticks, thinly sliced

3 carrots, thinly sliced

1 leek, trimmed and thinly sliced

1.5 litres (2½ pints) vegetable stock

400 g (13 oz) can chopped tomatoes

2 tablespoons tomato purée

½ tablespoon ground turmeric

½ teaspoon ground ginger

1 tablespoon coriander leaves

pepper