Heat 2 tablespoons of olive oil in a large skillet over medium heat.
Once the oil is simmering, add onion, and cook, stirring frequently, until translucent, about 2-3 minutes. Remove from heat and set aside.
In a large bowl, combine ground beef, ground pork, Panko bread crumbs, egg yolks, allspice, nutmeg, parsley, red pepper flakes, garlic powder, and cooked onion. Season with salt and pepper, to taste. Stir until well until combined.
Roll the mixture into 1 1/4-to-1 1/2-inch meatballs, forming about 24 meatballs and arrange them on a cutting board or large, flat plate.
Place the skillet over medium-high heat again and add the remaining 2 tablespoons olive oil. Once simmering, add meatballs, in batches, and cook until browned on all sides, about 4-5 minutes. Transfer to a paper towel-lined plate.