Wash the zucchini thoroughly and use a vegetable peeler or mandoline to create long, thin ribbons from top to bottom.
Place the zucchini ribbons on paper towels and gently pat them dry to remove excess moisture before adding them to the jars.
Add garlic cloves, dill sprigs, peppercorns, and mustard seeds into clean glass jars.
Carefully roll the zucchini ribbons and place them inside the jars, allowing them to fit loosely without being compressed.
Warm vinegar, water, salt, and sugar in a saucepan until the brine becomes clear and the seasonings dissolve.
Pour the warm brine over the zucchini ribbons, ensuring they are fully covered before sealing the jars.
Refrigerate for at least 12 hours before eating, then enjoy the ribbons as a topping for sandwiches, salads, or grilled dishes.