Preheat the broiler and set a rack in the top position. Line a baking sheet with aluminum foil for easy clean up.
Toast the English muffins under the broiler for about 1 minute on each side, or until golden brown and crisp on the top and bottom.
Arrange the muffins cut side up on the prepared baking sheet. Spoon a generous tablespoon of pizza sauce over each muffin half. Top with the mozzarella cheese and pepperoni. Sprinkle with the Parmigiano Reggiano cheese and oregano.
Place the pizzas under the broiler for a few minutes, or until the cheese is melted, bubbling and slightly golden. Serve warm.
Freezer-Friendly Instructions: These pizzas can be frozen for up to 3 months. Let them cool completely, then wrap them individually in plastic wrap or foil and place in a resealable bag. Reheat them (directly from the freezer) in a 375°F oven for 10 to 15 minutes, or until heated through.