Preheat the oven to 400˚. Spread the walnuts in a pie plate and toast for 6 minutes, until fragrant. Let cool, then chop. In a small bowl, mash the goat cheese with the lemon zest, garlic and half of the walnuts; season with salt and pepper. Using a small knife cut a pocket in the side of each chicken breast; keep the pocket opening as small as possible. Stuff the chicken breasts with the mixture and gently press to flatten them.
In a large ovenproof skillet, heat the olive oil until shimmering. Season the chicken with salt and pepper and cook over moderately high heat, turning once, until browned, about 6 minutes. Transfer the skillet to the oven and roast the chicken for 5 minutes. Transfer the chicken breasts to a platter and keep warm.
Add the lemon juice and stock to the skillet and cook over moderately high heat, scraping up any browned bits stuck to the pan. Simmer for 3 minutes. Stir in the walnut oil, parsley and the remaining chopped walnuts. Transfer the chicken breasts to plates, spoon the walnut sauce on top and serve. Servings: 4 Adapted from FoodandWine.com