Add the leeks, garlic, green onions and ginger to the pan and saute for 1 minute, stirring often. Add the tomato paste and stir well to incorporate. Sprinkle the flour over the vegetables and stir to combine. Cook, stirring for 3 minutes. Add the Guinness to the Dutch oven and increase the heat to medium-high. Bring the Guinness to a boil and cook for 5 minutes. Add the stock and allspice, stir, and return the turkey legs to the pan. Return the pan to a boil and reduce to a simmer. Cover and continue to cook the turkey legs until tender, about 2 to 2 1/2 hours. Remove the lid, and stir the chopped parsley into the pan. Serve immediately over steamed white rice.