Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it.
In a large bowl, combine the ground beef, breadcrumbs, grated Parmesan cheese, whole milk, egg, minced garlic, chopped onion, chopped parsley, salt, black pepper, and dried oregano.
Mix all the ingredients gently with your hands or a spoon until just combined. Do not overmix to keep the meatballs tender.
Shape the mixture into 1 1/2-inch meatballs and place them evenly spaced on the prepared baking sheet.
Heat the olive oil in a large skillet over medium-high heat. Add the meatballs in batches and cook for 2-3 minutes on each side until browned all over.
Transfer the browned meatballs back to the baking sheet and bake in the preheated oven for 15-20 minutes, or until cooked through and internal temperature reaches 160°F (71°C).
Remove the meatballs from the oven and let them rest for 5 minutes before serving.