01 - In a large bowl, combine ground beef, Italian seasoning, garlic powder, salt, and black pepper. Mix gently until just incorporated, then shape into 4 equal-sized patties about 3/4 inch thick. Press a small dimple in the center of each patty to prevent puffing during cooking.
02 - Heat olive oil in a skillet or grill pan over medium-high heat. Place the patties in the pan and cook for 4-5 minutes per side, or until a meat thermometer reads 160°F and the juices run clear. Transfer to a plate and tent loosely with foil.
03 - Set your oven broiler to high. Arrange the bottom halves of the burger buns on a baking sheet. Spread 1 tablespoon of pizza sauce evenly over each bun bottom.
04 - Place one cooked patty on each sauced bun bottom. Spoon another tablespoon of pizza sauce over each patty, then layer with shredded mozzarella cheese, pepperoni slices, sliced red onion, and sliced bell pepper.
05 - Slide the baking sheet under the broiler for 1-2 minutes, watching closely, until the cheese is fully melted and bubbly with golden spots on the pepperoni.
06 - Remove from the oven and garnish with fresh basil leaves and red chili flakes if desired. Cap each burger with the top bun half and serve immediately with extra pizza sauce on the side for dipping.