Prep the squash, small size can be just sliced into ¼ inch thick rounds. For large diameter, slice into ¼ inch rounds then cut slices in half. And for larger size, slice into ¼ inch rounds then cut slices into quarters. (I used 2½ of my garden grown yellow zucchini.)
Melt the butter in a large non stick pan (12 inch would be perfect), when hot, add the onion. Sauté onion until translucent.
Add the sliced squash on top of the onions, turn heat to low, cover the pan but stir after a few minutes and often after that. The squash will steam and they will begin to release their water.
When the squash cooks down a bit and water has been released, season squash with salt and black pepper as desired.
Continue to cook down the squash until the water is mostly cooked out.
When the squash is nearly falling apart, drain well in a colander.
Preheat your oven to 180° C (350° F) and grease a 9x13 baking pan with butter or cooking spray.
Add the squash to a large mixing bowl, then add the sour cream and soup.
I added a variant, I diced a can of spam, and added that.
Mix together, taste, season with salt and black pepper as desired.
Pour squash into the prepared pan and spread out evenly.
Cover with foil and bake for 30 minutes. Remove the foil, top with the Cheddar cheese, then the French fried onions.
Return to the oven, uncovered, for 10 minutes or until the onions are lightly browned.
Serve and enjoy.