Preheat oven to 425°F.
Cut tenderloin into 12 slices. Pound slices to flatten slightly. Mix flour, salt and pepper in shallow dish. Beat egg in second dish, with 1-3 Tbsp. water. Combine breadcrumbs with Italian seasoning in third dish. Dredge each meat medallion in seasoned flour, shaking off excess. Dip into egg wash to coat completely, then into seasoned crumbs, pressing crumbs to adhere to meat evenly.
Shallow-fry medallions in olive oil over medium heat in skillet until browned on both sides, then transfer to shallow baking pan in single layer. Cut each BelGioioso Fresh Mozzarella Bocconcini into thirds. Place one slice of cheese on each browned meat medallion, then top with 1 Tbsp. marinara sauce. Bake until cheese melts, about 10 minutes.