For the cucumber boat, cut a lid off the cucumber lengthwise. Hollow out the cucumber with a spoon.
Serrate the edge with a knife. Peel the apple, remove the core. Peel skin from four tomatoes, dice with apple and gherkin.
Mix yogurt with mustard, onion, lemon juice, sugar, salt and pepper, pour over the fruit cubes, mix loosely, season to taste and fill into the cucumber boat.
Wash and quarter the remaining tomato. Place on 2 wooden skewers as bow and stern sails. Place cheese bent into a sail on a wooden skewer and place a cocktail cherry at the tip.
Skewer the sail in the middle of the cucumber boat and the tomato sails at the ends of the boat.