In a mixing bowl, combine the lean ground beef, finely chopped onion, garlic powder, Italian seasoning, sea salt, and freshly ground black pepper. Mix gently until all ingredients are evenly incorporated. Avoid overmixing, as this can make the burgers tough.
Divide the beef mixture into four equal portions and shape them into patties. Make a small indentation in the center of each patty with your thumb to help them cook evenly and prevent puffing up.
Heat the olive oil in a skillet over medium-high heat. Once hot, add the burger patties. Cook for about 4-5 minutes on one side until browned, then flip and cook for another 3-4 minutes. During the last minute of cooking, place a slice of mozzarella cheese on each patty to melt.
While the burgers are cooking, mix the softened butter with minced garlic and chopped parsley in a small bowl. Spread this mixture on the inside of each hamburger bun. Toast the buns in the skillet or under the broiler until golden brown.
Spread a generous amount of pizza sauce on the bottom half of each toasted bun. Place the cheesy burger patty on top, followed by three slices of pepperoni and a sprinkle of fresh basil. Top with the other half of the bun.
Serve your Pizza Burgers immediately with extra pizza sauce on the side for dipping. Enjoy the burst of flavors and share with friends and family!