Heat 2 tbsp (30 mL) oil in a large skillet on medium. Add onion and cook until soft; approx. 10 min. Add garlic and cook for 1 min. longer. Transfer onion and garlic mixture to a small bowl and let cool.
Place bread pieces in a small bowl and cover with milk. Allow to soak for a few minutes. Meanwhile, combine beef and pork in a large bowl. Gently break meat into smaller pieces with hands. Add egg, parsley, salt, pepper, reserved onion and garlic, bread and cheese. Mix until well combined.
Using a 1/4 cup (60 mL) measure, scoop meat mixture and roll into 16 balls. Place on baking tray. Heat remaining olive oil in skillet on medium. Working in small batches, add meatballs and brown on all sides, then cook 15 to 20 min. or until internal temperature reaches 160°F (71°C) on an instant-read thermometer. Remove meatballs from pan and place on paper towel to drain.