Preheat the oven: Set your oven to 425°F and allow it to fully preheat before starting the chicken.
Prepare the chicken breasts: Dry the chicken breasts with paper towels, then carefully cut a horizontal pocket into the thickest part of each one. Season the outside of each breast, as well as the inside of the pocket, with ½ teaspoon of kosher salt and ½ teaspoon of freshly ground black pepper.
Prepare the walnut butter filling: Using a mini food processor or a mortar and pestle, combine the toasted walnuts, bread pieces, butter, thyme leaves, lemon zest, garlic, allspice, 1 teaspoon of kosher salt, and 1 teaspoon of black pepper. Blend or crush the mixture until it forms a smooth paste. If you’re using a larger food processor, pause occasionally to scrape down the sides so everything blends evenly.
Stuff the chicken: Gently spread a portion of the walnut butter under the skin of each chicken breast. Then, use the remaining filling to stuff the pocket you created in the meat. Place the stuffed chicken breasts on a baking sheet with the skin side facing up.
Roast the chicken: Put the baking sheet in the oven and roast the chicken for about 25 minutes. The chicken is ready when the meat is fully cooked through, and the skin is crisp and golden.
Make the glaze: In a small bowl, mix together the pomegranate molasses, olive oil, and a generous pinch of salt and pepper. If the glaze feels too thick, add a small amount of water to thin it out to a drizzling consistency.
Finish and serve: Drizzle the prepared glaze over the chicken breasts right before serving. If desired, garnish with fresh chives and a sprinkle of pomegranate seeds to enhance the presentation.