Preheat the oven to 200 degrees Celsius (400 degrees Fahrenheit). Line a large baking sheet with parchment paper.
In a small bowl, combine the bread crumbs and milk. Set aside.
Set a frying pan over medium heat. Add in the bacon and fry for several minutes, until oil is rendered from the fats, 2-3 minutes. Turn the heat down to medium low and add in the onion and garlic. Stir-fry until the onion has softened and the bacon is slightly crispy (too crispy and they will be too hard to chew later on), about 4-5 minutes. Remove from heat and let cool slightly.
Combine bacon mixture, chicken, pork, parsley, Parmesan cheese, 2 tablespoons tomato paste, egg, oregano, black pepper and salt in a large mixing bowl. Drain the bread crumbs, squeezing it lightly to get rid of excess milk, and add into the mixing bowl. Discard the excess milk. Stir the mixture with a large metal spoon (or use your hands) and mix thoroughly. Shape the mixture into 1.5-inch large meatballs. Place them on the lined baking sheet.
Combine the remaining 2 tablespoons tomato paste with the olive oil. Brush the mixture over the meatballs.
Bake the meatballs for 20 - 25 minutes until fully cooked through.