For the cucumber soufflés, peel the cucumber and cut into coarse pieces. Puree together with the cream cheese. Season with 8 finely chopped basil leaves, salt and pepper.
Beat the egg whites to a firm snow and carefully fold into the cucumber puree.
Peel, core and dice the tomatoes.
Heat 1 tablespoon of olive oil in a pan and roast the onions until golden. Add the diced tomatoes, salt, pepper and simmer on low heat for about 15 minutes.
Grease 4 ramekins with butter. Pour a tablespoon of the tomato mixture into each mold and fill 2/3 full with the cucumber mixture.
Fill a deep baking sheet or large baking dish with boiling water and place the ramekins inside. Bake the cucumber soufflés in a preheated oven at 200 °C for about 15 minutes.
Remove the cucumber soufflés, garnish with a basil leaf and serve immediately.