Slice the zucchini very thinly, e.g., with a peeler.
Wrap the mozzarella balls in the slices and layer the rolls close together in a canning jar (500 ml). Spread the basil leaves and the mustard and peppercorns in between. The clove of garlic can be added whole or cut into small pieces, depending on your taste.
Pour olive oil on until everything is covered, put in a cool place and let steep for at least two days.