In a medium sized bowl, combine ground beef, onion, garlic, parmesan, parsley, salt, and pepper. Using your hands, mix ingredients together until combined, being careful not to over-mix.
Form beef mixture into four equal sized patties.
Place a thick slice of mozzarella in the middle of one patty, then cover with a second patty. Tightly squeeze the edges around the cheese to seal the patty. Repeat with the remaining patties and cheese. You should have two (1/2 lb.) cheese-stuffed patties.
Heat a medium saucepan over medium heat and add 2-3 tbsp. olive oil. Add patties and brown on each side, turning once after about 4 minutes.
When both sides are browned, add marinara sauce to pan and cover, simmering for another 5-7 minutes, flipping burgers halfway through and re-coating with sauce.
Serving the stuffed burgers on Martin’s Sandwich Potato Rolls, atop a bed of arugula, with more grated parmesan and parsley to garnish.