Add the ground beef to a large bowl. Using a box grater, grate the onion directly into the bowl (so the extra juice goes in there too). Add the garlic, parmesan, italian seasoning, salt and pepper. Use your hands to mix everything together. Mix until everything is just combined without overworking the meat.

Divide mixture into 4 portions. Gently shape into a disc about 1/2-inch thick and 4 inches across. Resist the urge to shape the edges perfectly. The less we mash, the more tender the burgers will be!

Meanwhile, heat a large cast iron skillet over medium-high heat. Spray with a little cooking spray. Wait a few minutes and then once hot add the burgers. Cook for 4 minutes. Then flip the burgers.

Sprinkle the cheese on top (about 3 tablespoons each burger). Add 3 slices pepperoni to each. Cook for another 2-4 minutes, or until burgers are cooked to liking (see burger temperature guide in notes).

Toast buns with a little olive oil if desired (I like to broil on high for 2-3 minutes). Spread one tablespoon of pizza sauce on the bottom bun. Add the burger patty, fresh basil leaves and top bun. Serve with extra pizza sauce if desired and enjoy!