In a bowl, mix by hand the beef, sausage, salt, pepper, Italian seasoning, and garlic powder. Form the meat into 4 burger patties. Set aside.
Pre-heat grill to medium-high heat. Using a tongs, place pepperoni on the grill. Cook for about 30-45 seconds and flip. Remove from grill and set aside.
Butter both sides the buns. Place buns quickly on the grill to get a light toast. Be certain not to leave them on more than 20-30 seconds because they will burn. You can also toast them on a skillet or in the oven as well.
Place burgers on the grill. Grill 4 minutes, and then flip. Wait an additional 4 minutes, and check the temperature of the burgers. The burgers should be 160°F before removing from the grill. Just before you remove the burgers add a slice of mozzarella to each burger and allow a few minutes for it to melt. Remove burgers and allow them to rest 2-3 minutes.
Spread 1 tablespoon of pizza sauce on the bottom bun. Follow with the burger, and then with 2 slices of grilled pepperoni. Top with additional sauce and bun. Serve and enjoy!