1. Place the eggplant on the grate of a gas burner over a high flame. Char the eggplant, turning it every few minutes, until the skin is blackened and the flesh is cooked through; this should take about 12 minutes. (Alternatively, you can char the eggplant on a barbecue grill, on a grill pan, or on a baking sheet under the broiler of a gas or electric oven.) Allow the eggplant to cool slightly, and then cut it in half. Scrape out the flesh, being careful not to incorporate the blackened skin. Measure out ¼ cup of the flesh; reserve the remaining eggplant for another use.
2. Bring a large pot of salted water to a boil. Meanwhile, in a small sauce pot, heat the marinara sauce over medium heat.
3. In a blender, combine the chicken broth, onions, garlic, cooked eggplant, and egg white. Puree until the mixture is smooth. In a large bowl, combine the pureed mixture with the ground turkey, parsley, and 2 tablespoons of the cheese. Season lightly with salt and pepper. Divide the meat mixture into 8 equal portions, a little over 2 ounces each.
4. When the marinara sauce comes to a simmer, roll each portion of the meatball mixture with the palms of your hands to form a ball, and gently drop the meatballs, one by one, into the hot marinara sauce. Shake the pan gently to coat the meatballs with sauce. Cover the pan, and when the sauce begins to simmer, reduce the heat to low. Simmer the meatballs for 12 minutes. Gently turn each meatball over in the marinara sauce and simmer for another 5 minutes.
5. While the meatballs are cooking, cook the pasta in the boiling water according to the package directions, about 10 minutes; drain.
6. Divide the spaghetti among 4 plates, and top each plate of pasta with 2 meatballs and some sauce. Sprinkle the remaining 4 tablespoons cheese on top, and serve.