In a large bowl, combine the turkey, panko, egg, Parmesan, garlic, Italian seasoning, salt and pepper. Mix gently with your hands just until combined, then roll into 16 meatballs, about 2 tablespoons each.
Heat the olive oil in a large skillet over medium-high heat. Add the meatballs and cook, turning, until browned on all sides, about 8 minutes total; they will not be cooked through yet.
Pour the marinara over the meatballs, lower the heat, cover and simmer 12-15 minutes, until the meatballs are cooked through and register 165 °F on an instant-read thermometer.
Meanwhile, cook the spaghetti in salted boiling water according to package directions. Drain, reserving 1/2 cup of the pasta water.
If the sauce looks thick, stir in a splash of the reserved pasta water. Serve the meatballs and sauce over the spaghetti, topped with torn basil and extra Parmesan.
