Preheat oven to 400
Brush the bottom of a medium size baking dish with refined coconut oil or butter.
Slice zucchini and onion with a knife or mandoline Buy a Mandoline here and set aside. In a small bowl mix together melted butter, grated garlic, basil, salt and pepper, set aside.
Start layering the zucchini in the bottom of the casserole dish like pictured above. When you get the first layer down sprinkle with a little salt and pepper, then a sprinkle of mozzarella and fresh parmesan, and a few slices of onion (putting smaller amounts of cheese in-between the layers and saving a larger amount to go on top.)
Repeat layer with zucchini, salt, pepper, and cheeses and onion ending up with the remaining of your cheeses on top. ( You should end up with 3-4 layers of zucchini depending on how big your zucchini is.)
Pour the melted butter/spice mixture evenly over the top.
With a spoon, place dollops of marinara along the edges of the dish.
Cover and bake 45 minutes.
Uncover, turn on the broiler and cook under broiler for 5-10 minutes or until nicely browned.
Enjoy!