Stir oil and flour together in a large, heavy-bottomed pot over medium heat. Cook, stirring slowly and constantly to keep the roux from burning, until the mixture becomes a dark chocolate brown, about 25 minutes. Add the onions, celery, and bell peppers to the roux all at once, and continue to stir until vegetables are wilted, about 5 minutes. Season with salt and cayenne pepper.
Stir in the smoked sausage and bay leaves, and continue to stir for 3 to 4 minutes. Pour in the turkey stock and stir until the stock and roux mixture are well combined. Bring the gumbo to a boil, then reduce heat to medium-low. Cook, uncovered, stirring occasionally, for 1 hour. Stir in the turkey and the file powder; simmer for 2 hours.
About 30 minutes before serving, bring the rice and water to a boil in a saucepan over high heat. Reduce heat to medium-low, cover, and simmer until the rice is tender, and the liquid has been absorbed, 20 to 25 minutes.
Skim off any fat that rises to the surface of the gumbo; remove from heat. Stir in the parsley and green onions. Remove the bay leaves, and serve the gumbo in deep bowls with rice.
