four 10-ounce ovensafe bowls or crocks with a little lip
Heat a medium pot over medium heat. Add the pepperoni and oil and saute until the fat renders out and the pepperoni is slightly caramelized, about 10 minutes. Add the Italian seasoning and garlic and saute until fragrant, about 10 seconds. Add the crushed tomatoes and salt and pepper to taste; stir and simmer for about 15 minutes. Let cool completely.
Preheat the oven to 400 degrees F with a rack in a lower position.
Spray the insides of four ovenproof bowls or crocks with plenty of cooking spray. Shingle 6 to 8 slices cheese inside each bowl so the bottoms touch. This creates the coveted cheese bowl effect. Place 3 to 4 mushrooms on top of the cheese. Then ladle about 1/2 cup COOLED pepperoni sauce over the mushrooms.
Split the dough into 4 equal portions and roll each portion out on a lightly floured surface into 6- to 8-inch rounds. (You will want a 1-inch overhang over the side of the bowl.)
Drape a round of dough on top of each bowl. Spray your fingertips with cooking spray and slide them around the outside edges of the bowls so that the pizzas will slide out easily after baking. Gently pull down and press the dough around the edges to create a seal. (There's no need to vent or dock it.) Place the bowls on a sheet pan.
Bake until the crust is just SLIGHTLY golden, about 15 minutes. Let cool 5 minutes, then brush the tops with melted butter to make that crust shiny! Very gently and carefully turn over a bowl into an individual bowl or plate. Take the handle end of your fork and swipe around the inside of the crust rim to help loosen and separate it from the bowl. Lift the bowl away and witness the miracle of this cheesy behemoth. Top with some giardiniera, if you like. Repeat with the remaining pot pies.