Prep the buns. In a small bowl, mix together butter and garlic cloves. Brush the mixture on both sides of all the buns. Set aside.
Prep the burgers. Divide the beef into four equal sections and use your hands to gently shape each section into a ball. Use the palm of your hand to press each ball into a burger shape. It doesn’t have to be perfectly round. Press your thumb into the center of each burger to prevent doming.
Season. Mix together the salt, pepper, and garlic powder in a small bowl. Sprinkle both sides of the burgers with the seasoning mixture.
Fry the burgers. Heat a cast iron skillet over medium high heat and add just enough vegetable oil to coat. When the oil shimmers, place the patties in the skillet. Fry about 3 minutes or until liquid starts to pool on the top of the burgers, then flip and fry an additional 2-3 minutes or until internal temperature reaches desired doneness (see temp chart below). Place a slice of mozzarella on the burgers for the last minute and cover with a lid or sheet pan to allow it to melt. Remove the burgers to a plate and loosely tent with foil.
Broil the buns. While the burgers are frying, place the buns buttered side up on a baking sheet and broil for 3-4 minutes. Some will likely brown quicker than others, so you might have to remove some sooner and let the others continue to brown another minute or so.
Assemble. To assemble the burgers, spread both sides of the toasted garlic buns with the marinara. Top the bottom bun with the burgers and fresh basil leaves and sandwich with the top bun.