Wilt Spinach in a pan over medium heat, drain in colander to remove excess liquid. Place in bowl add bread crumbs and S&P while mixing with hand until desired consistency and seasoning is achieved.
Place pork loin perpendicular to yourself on the cutting board and with a sharp knife make an incision ¾ of an inch high all the way down the loin. Continue going back over this incision while simultaneously rolling the loin with your opposite hand to achieve a flat piece of meat
Lay the seasoned spinach mixture evenly over the pork and sprinkle with fresh garlic to taste. Place the sliced mozzarella on top of the spinach in a single layer.
Starting from the inside piece of the pork roll back up tightly to the porks original shape. Using butchers twin tie the loin tightly every inch so loin is uniform.
Place loin on a sheet tray with a rack and roast off at 300* on low convection until internal temp reaches 140*. Remove and let set for at least 45 minutes.
Slice into ¾ inch pieces and fan out on serving tray or plate, cascade 1-2oz marinara per slice