Will made a version of this for one of the potluck’s in 2018. It was a huge hit, and simple!
In his version, he left out the squash and didn’t cover it with foil to bake to get rid of moisture. He also added a slice of cheese to each layer in the center. The cheese melted into the whole dish and gave it a ton of flavor!
https://www.simplyrecipes.com/recipes/zucchini_eggplant_tomato_gratin/