Pepperoni Pizza Sliders

Name: Pepperoni Pizza Sliders
Prep time: 5 min
Cook time: 15 min
Total time: 20 min
Cuisine: American
Ingredients: one 12-count package Hawaiian sweet rolls (sliced in half (see directions for more details)); 1 cup pizza or marinara sauce; about 2 1/2 cups shredded mozzarella cheese (divided); one 5-ounce package mini pepperoni (regular size may be substituted); 1/2 cup unsalted butter (melted (1 stick)); 2 tablespoons dried minced onion; 2 tablespoons freshly grated Parmesan cheese (plus more for garnishing to taste); 2 teaspoons dried oregano; 3/4 teaspoon garlic powder (or to taste); 1/2 teaspoon kosher salt (or to taste); 1/4 teaspoon freshly ground black pepper (or to taste); 1 tablespoon finely chopped fresh Italian flat-leaf or regular parsley (optional for garnishing)