Toast The Walnuts: Heat the oven to 375°F and arrange a rack in the middle. Spread the walnuts on a rimmed baking sheet, and toast until golden and toasted smelling, about 8 to 10 minutes. Remove from oven until cool enough to handle then pulse in a food processor until ground into a fine meal.
Prepare The Chicken: Meanwhile, use a paper towel to pull off any skin and any excess fat from the chicken thighs. Mix together the coriander, cinnamon, 1 1/2 teaspoons of the salt, and 1/2 teaspoon fresh ground black pepper and rub into the chicken thighs.
Simmer The Pomegranate Sauce: Combine the pomegranate juice and brown sugar in small saucepan. Bring to a boil and let cook until reduced by half, about 30 minutes. When the juice is reduced, remove from heat and set aside.
Sear The Chicken: Meanwhile, begin cooking the chicken. Heat the butter and oil in a large, heavy-bottomed saucepan or Dutch oven over medium-high heat. When the butter foams, add chicken to the pan, working in batches, so its in a single layer and not crowded. Cook chicken until its golden brown on both sides, about 2 minutes per side, or until golden and seared. Remove the chicken from the pan and set aside. Repeat with remaining chicken.
Cook The Onions: Remove and discard all but 1 tablespoon of the oil mixture from the pan. Add onions to the pan, reduce heat to medium, season with the remaining 1 teaspoon of the salt, and stir to coat. Cook, stirring occasionally, until onions are golden brown, about 5 minutes.
Braise The Chicken: Add the reduced pomegranate juice mixture, ground toasted walnuts, and chicken. Cook on low heat for 1 hour, stirring every 5 minutes to prevent the walnuts from sticking to the bottom of the pan. Check to make sure the sauce is thickened and the chicken is cooked through and knife tender.
Garnish The Stew: Remove from heat and adjust sugar and salt to taste. Serve over grains and garnish with walnuts, pomegranate arils, and parsley.