Close family friend who has shared many great italian recipes gave this to Mom years ago. Still our all time way to cook zucchini. Up to you about how many layers to use. You can use italian seasoning in place of oregano, if you like.
In reserved fat, saute onions until cooked, remove & set aside on a paper towel. Add zucchini to pan & saute until cooked, drain on paper towel. In casserole layer- zucchini, onion, salt & pepper, oregano, bacon & dot with ketchup. Continue until all are used. Finish with bacon & ketchup. Bake at 350@ for 20-30 minutes until hot & bubbly.