Heat the oil in a large saucepan, add the onion and cook gently for 5 minutes until softened. Stir in the curry paste and cook gently over a low heat for 3 minutes.
Add the pumpkin and stir to coat with the onion mixture. Stir in the apple and tomatoes. Pour in the vegetable stock and bring to the boil. Reduce the heat, cover and simmer for 25 minutes, or until the pumpkin is tender.
Meanwhile, to make the croûtons, cut the crusts off the bread and cut the bread into small cubes. Heat the oil in a non-stick frying pan, then sauté the bread cubes until golden and crispy all over. Drain on paper towels.
Allow the soup to cool slightly, then purée it in a blender or a food processor until smooth. Reheat gently, season to taste and stir in the chopped coriander. Serve with a scattering of croûtons and coriander leaves.
If you are buying a wedge of pumpkin to make this soup, you'll need about 1.25 kg to give 600 g flesh.