In a medium bowl, combine the ground beef, oregano, garlic powder, salt, and pepper.
Form the mixture into four equal patties, approximately 3/4-inch thick.
Heat a large skillet or griddle over medium-high heat.
Cook the patties for 4-5 minutes per side until the internal temperature reaches 160°F (71°C).
While burgers cook, butter the buns and toast them on a separate pan until golden brown.
Top each cooked patty with 2 tablespoons of marinara sauce, 1/4 cup of mozzarella, and 4 pepperoni slices.
Place a lid over the skillet for 1 minute to melt the cheese.
Place the patties onto the toasted buns and serve immediately.