Squash (that is what zucchini is after all), does not can well without being mushed. An example is canned pumpkin. Squash is water based and to can it, you have to cook it which in turn makes it mushy. Even freezing it will not work because the water in it crystallizes when frozen which then makes the squash break down when you heat it up or let it thaw.
To make canned Zucchini not to turn to mush, you have to freeze it. This way , it will preserve its original texture for a reasonable duration of time. However, you should not keep it mixed with other fruits you had prepared since it will lose the test.