Heat the oven to 425°F (220°C) and line a baking sheet with parchment paper or lightly oil it. In a large bowl, combine the ground beef, ground pork, breadcrumbs, Parmesan, egg, garlic, parsley, Italian seasoning, salt, and pepper.

Mix the meat mixture gently with your hands just until the ingredients are combined. If it appears dry or difficult to shape, add the milk, then chill the mixture for 15–20 minutes if time allows.

Shape the mixture into approximately 20–24 meatballs, each about 1 1/2 inches (4 cm) wide. Arrange them on the prepared baking sheet with a little space between each one.

Bake the meatballs for 15–18 minutes, turning them once if desired, until browned and cooked through. Check that the centers reach 160°F (71°C); alternatively, brown them in 1 tablespoon olive oil in a skillet, cover, and cook until done.

Whisk the olive oil, red-wine vinegar, Dijon mustard, garlic, oregano, salt, and pepper in a bowl or shake them in a jar. Add 1–2 tablespoons water if the vinaigrette needs to be loosened.

Place the romaine or mixed greens in a large serving bowl and add the tomatoes, cucumber, red onion, olives, pepperoncini, mozzarella, and fresh herbs. Toss with most of the dressing immediately before serving.

Top the dressed salad with warm or slightly cooled meatballs, then finish with the shaved Parmesan and remaining vinaigrette. Serve promptly while the greens are crisp and the meatballs are still pleasantly warm.