Preheat your oven to 400 F/200 C. To a bowl, add the ground beef, parmesan, mozzarella, the egg, salt, and ½ tsp black pepper. Chop the parsley and add most of it in, reserving the rest as garnish.
Combine the meatball ingredients until everything has come together. Divide into 20 portions and roll them into meatballs. Add 1 tbsp butter to a skillet and place it over medium-high heat.
Cook the meatballs in the skillet until browned on all sides. You may have to do this in 2 or 3 batches. Return all the meatballs to the skillet and transfer them to the oven.
Bake for 10-15 minutes until the meatballs are fully cooked. Take them out of the skillet and let the rest. Meanwhile, use a spiralizer to make zucchini noodles. Add 1 tbsp of butter to a clean pan and place it over medium-high heat.
Add the zoodles and cook for 3-4 minutes until just softened. Season with black pepper and toss. Don’t season with salt at this stage because it will cause the zucchini to release water.
Divide the zucchini noodles into 4 bowls. Top with 5 meatballs. Garnish with the remaining parsley, season the zoodles, and serve!