Cut the watermelon into slices about 2 inches thick. Using a pastry cutter, form 12 small cylinders and, using a smaller one, remove the middle part to make space for filling.
In a small bowl, process the goat cheese with the tablespoon of oil, adding the finely chopped mint and a grinding of pepper.
Prepare the sac a poche by inserting the large-hole spouted nozzle and fill it with the cream cheese. Dry the watermelon cylinders with paper towels and fill them with the cream cheese.
Arrange them in a nice serving dish and finally decorate with the cucumber halves. Serve immediately.