Chicago Pizza Pot Pie

Name: Chicago Pizza Pot Pie
Ingredients: One 8- to 10-ounce stick pepperoni, casing removed, cut into small cubes; 1 tablespoon olive oil; 1 teaspoon dry Italian seasoning; 2 cloves garlic, minced; One 28-ounce can crushed tomatoes; Kosher salt and freshly ground black pepper; Nonstick cooking spray, for the bowls; 24 to 32 deli mozzarella slices (about 2 pounds); 12 to 16 baby bella mushrooms, left whole; 1 pound pizza dough (store-bought is great!); All-purpose flour, for rolling; 2 tablespoons unsalted butter, melted; Hot giardiniera, for topping, optional