I have no idea where the original for this came from. But I’ve been making it in one form or another for years. I have changed the amount of potato over the years. Originally I think the layers went potato, onion, potato, zucchini, etc but that’s way more starch than I like these days.
Zucchini Layers
Preheat your oven to 425.
Peel one medium russet potato. Thinly slice the potato, two zucchinis and one medium onion. Cut the onion in half first.
Layer, slightly over lapping, on a parchment papered sheet. Your call on the layers.
I do zucchini, onion, zucchini, potato, zucchini, etc. Top with dill Havarti cheese, shredded.
Baked 30-40 minutes, it depends on the thickness of your slices, until done. 
T.A. Henry 