In a large bowl combine ground beef, ground veal, ground pork, breadcrumbs, parsley, egg, milk, minced garlic, salt, and pepper. Mix well using your hands. Roll the meat mixture into 2inch balls. Press a cube of provolone cheese into the center of each meatball and seat it inside.
Heat olive oil in a large skillet over medium-high heat. Add the meatballs and cook until browned, about 1 minute per side. Transfer to a plate lined with paper towels. Pour the marinara sauce into a sauce saucepan and bring to a simmer over medium-high heat. Add the meatballs and reduce heat to medium-low. Cover and simmer until cooked through (the internal temperature has reached 160 degrees F), about 30 minutes.
While the meatballs are cooking, cook fettuccini pasta according to package directions. In a medium saucepan heat the alfredo sauce over medium-low heat.
Drain the noodles and toss them with the alfredo sauce. Serve the meatballs on top of the alfredo noodles. Top with fresh parsley and parmesan cheese if desired.