Preheat oven to 425°F.
Place meats in a large bowl and season with salt and pepper. Grate 3-4 tablespoons of onion over the meat then add garlic, grated cheese, mint, parsley, lemon zest and egg yolks. Squeeze out the excess milk from the breadcrumbs and add them to the bowl along with the EVOO. Combine meatball mixture and roll into 2-inch balls using small scoop. Arrange meatballs on a parchment-lined baking sheet and bake to brown and cooked through, about 15-18 minutes.