I have used large zucchini in Mock Apple Pie as well.
I peel the zucchini, then split the zucchini in half long ways, run a melon baller down the center of each halve, taking out the seeds. Then I slice across the halves.....about as thick as you would when slicing apples for pie.
I add a small amount of apple juice to the raw zucchini slices and microwave for a few minutes. I then proceed with regular apple pie recipe. This is a good way to use up the large zucchini towards the end of the season.