In a large bowl, mix together ground turkey, panko, garlic, egg ¼ cup grated parmesan, ¼ cup parsley, salt, and pepper.
Form the mixture into golf ball-sized meatballs (you should be able to get about 28-30 meatballs).
Heat olive oil over medium-high heat in a large skillet and add meatballs. Cook, turning as needed, until browned, about 5-7 minutes. If you can’t fit all your meatballs in the skillet, you can cook them in two batches. Return all meatballs to skillet.
Add water to the skillet and simmer, being sure to stir on occasion, for about 10 minutes until the meatballs are cooked through (they should have an internal temperature of 165 degrees) and liquid is reduced to about ½ cup. Add tomatoes and cook for another minute.
While meatballs are cooking, boil pasta. Add it to a large pot of salted water and cook until just al dente. Drain and return to pot.
Add meatballs and tomatoes (along with liquid in pan), mozzarella, remaining parmesan cheese, remaining parsley, and butter. Toss to combine. Add more salt and pepper if desired.