You can use zucchini of any size; some larger zucchini or squash tend to get very seedy in the middle, so you can discard the core if the ribbons have too many seeds. We found that the grilled method works better with a little thicker slices of zucchini (around ⅛ inch); the raw method works well with very thin slices. The amount of dressing makes more than needed for zucchini; you can keep the leftovers refrigerated in the jar and use for salads.