Brown the Meat: In a skillet over medium heat, cook the ground beef, sausage, and onions until browned. Drain excess grease.

Transfer to Crockpot: Add the cooked meat to the slow cooker. Stir in pizza sauce, diced tomatoes, garlic powder, Italian seasoning, and red pepper flakes.

Slow Cook: Cover and cook on LOW for 4 hours or HIGH for 2 hours, stirring occasionally.

Melt the Cheese: In the last 15 minutes, stir in mozzarella cheese and allow it to melt.

Assemble the Burgers: Toast the buns, then spoon the pizza meat mixture onto each one. Top with pepperoni slices and Parmesan cheese if desired.

Serve & Enjoy! Pair with a side of fries, salad, or garlic bread.