Preheat oven to 350 degrees F. and pour olive oil into bottom of 8 inch cast iron skillet swirling to coat bottom of skillet.
Start layering zucchini slices into bottom of skillet. When one layer covers the bottom of the skillet, season zucchini slices with a pinch of salt, oregano and pepper. Continue this same method until all of your zucchini slices have been used. Spoon pizza sauce over zucchini slices, sprinkle with Parmesan cheese, then top even with shredded mozzarella cheese. Top with quartered pepperoni slices, sprinkle with a pinch or two more dried oregano and bake for 25-30 minutes, until cheese is bubbly and melted. Remove from oven, garnish with a sprig of fresh basil and serve hot by spooning onto serving plates. This pizza is not meant to cut into wedges. Also note, be cautious of the hot skillet handle. The cast iron skillet stays very hot for quite a long time.
Notes
Watch pizza carefully so that you don't overcook the zucchini. It's best slightly undercooked as it will continue to cook slightly in the hot skillet when removed from the oven.
Be careful when serving, the cast iron skillet stays hot for a while after it's removed from the oven.
Put a heat proof sleeve over the cast iron skillet handle to prevent burns when handling.