01 - Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
02 - Combine breadcrumbs and whole milk in a small bowl. Allow to soak for 2 minutes.
03 - In a large mixing bowl, gently mix ground beef, ground pork, soaked breadcrumbs, egg, onion, garlic, Cajun seasoning, salt, black pepper, and chopped parsley until just combined.
04 - Divide meat mixture into 16 equal portions. Flatten each portion, place a mozzarella cube in the center, then seal and roll into a ball.
05 - Heat olive oil in a large skillet over medium-high heat. Sear meatballs in batches for 2 to 3 minutes, rotating until evenly browned.
06 - Transfer browned meatballs to the prepared baking sheet. Bake for 15 to 18 minutes, or until cooked through and cheese is melted inside.
07 - If desired, warm marinara sauce and serve meatballs atop the sauce. Sprinkle with extra chopped parsley before serving.