Prepare the breadcrumb base. Heat the oven to 400°F (200°C), conventional heat. Lightly oil a rimmed baking sheet. In a large bowl, mix the breadcrumbs and milk and leave for 3 minutes so the crumbs absorb the liquid.

Add the seasonings. Stir the egg, Parmesan, garlic, oregano, salt, pepper, and parsley into the damp breadcrumbs. Breaking up the egg at this stage means less mixing is needed after the turkey goes in.

Mix and shape gently. Add the cold ground turkey and fold with a fork or clean hands just until combined. Divide into 20 equal pieces, roughly 1½ inches across, and roll gently. Arrange on the tray with a little space between them, then wash hands and raw-meat utensils.

Bake to a safe temperature. Bake for about 18–22 minutes, checking a few of the largest meatballs with a thermometer. Ground poultry must reach 165°F (74°C) in the center. If the meatballs vary in size, remove finished ones to a clean dish while the larger ones continue cooking.

Warm the marinara. While the meatballs bake, heat the marinara in a saucepan over medium-low heat, stirring occasionally. Let it become hot and gently bubbling, then lower the heat so it stays ready without splattering or reducing heavily.

Combine and serve. Place the safely cooked meatballs in the hot sauce and turn gently to coat for 1–2 minutes. Divide into four portions of five meatballs. Add optional extra parsley and serve with your chosen side.