Peel and deseed the cucumber and chop into 1cm/½ inch cubes. Blanch the tomatoes quickly in boiling water, skin and deseed them, then chop into pieces the same size as the cucumber. Chop the spring onions the same size, too. Mix the lot together with some sea salt and leave in a colander for about an hour to drain. Pat dry on kitchen paper, then place in a salad bowl.
Using a liquidizer