1. Heat the oil in a large saucepan. Add the onion and fry for 1 minute, stirring constantly. Add the cucumber to the pan and fry for 1 minute, stirring constantly. Pour over the stock and bring to the boil. Reduce the heat to low and simmer for 10 minutes, stirring occasionally.
2. Stir in the tomatoes and simmer for a further 5 minutes.
3. Remove from the heat and beat in the egg. Serve at once.
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