Preheat oven to 400°F. Line a baking pan with foil and coat with nonstick cooking spray.
Cook pasta as directed on package. Meanwhile, thaw spinach then squeeze out any excess liquid. Chop onion and mince garlic.
In a large bowl, stir together the egg and ketchup.
Stir onion, garlic, bread crumbs, salt, and pepper into the egg mixture; gently mix in the ground turkey (using your hands is messy, but usually works the best).
Divide turkey mixture into 16 1-inch round balls. Flatten each ball slightly, place 1 tablespoon spinach inside each, then roll back into balls.
Place stuffed meatballs onto prepared baking sheet and bake for 20-25 minutes until meat is no longer pink, turning at least once halfway through cooking.
While meatballs are baking, pour the marinara sauce in a small saucepan and heat over medium heat until warmed through.
Dice apples; chop lettuce, onion, and tomato. Toss all into a large bowl along with the dressing.
Serve meatballs and marinara over pasta with salad on the side.