01 - Preheat oven to 400°F. Grease a 9x13-inch baking dish with cooking spray or butter.
02 - Combine ground turkey, breadcrumbs, egg, Parmesan, garlic, parsley, oregano, salt, and pepper in a large bowl. Mix gently until just combined. Form into 1.5-inch meatballs (about 18-20) and arrange in the prepared dish.
03 - Pour marinara sauce evenly over the meatballs. Sprinkle with dried basil and red pepper flakes if using.
04 - Bake uncovered for 20 minutes.
05 - While meatballs bake, toss bread cubes with melted butter, minced garlic, and parsley in a large bowl until well coated.
06 - Remove dish from oven. Sprinkle mozzarella and Parmesan cheese over meatballs and sauce. Top with garlic bread cubes in an even layer.
07 - Return to oven and bake for 15 minutes, until bread cubes are golden and cheese is melted and bubbly.
08 - Let rest for 5 minutes before serving to allow flavors to meld.