In a large mixing bowl, combine the minced turkey breast, rolled oats, Parmesan cheese, egg, parsley, garlic, olive oil, dried oregano, salt, and pepper. Mix everything together with your hands or a wooden spoon until just combined. Be careful not to overmix.

Use your hands to shape the mixture into meatballs, about 1 1/2 inches (3.8 cm) in diameter. You should end up with around 12-15 meatballs.

Heat a large frying pan or skillet over medium-high heat. Add a small amount of olive oil to the pan and swirl it around to coat the bottom.

When the oil is hot, add the meatballs to the pan and cook for about 5-7 minutes on each side, or until they're browned and cooked through. You might need to cook them in batches depending on the size of your pan.

While the meatballs are cooking, heat the marinara sauce in a separate saucepan over low heat.

Once the meatballs are done, add them to the marinara sauce and simmer for a few minutes to coat them in the sauce.

Serve the meatballs hot, garnished with some extra parsley and a sprinkle of Parmesan cheese if desired. You can also add a sprinkle of shredded mozzarella cheese on top.

Store any leftovers in an airtight container in the fridge for up to 3 days or freeze for up to 2 months. Reheat them in the oven or microwave until hot and steaming.