Chicken and rice never looked so dazzling. Pomegranate seeds, tossed with basmati rice, are exceptionally high in antioxidants; juice adds sweet tartness to the chicken's glaze.
Combine rice, stock, and bay leaf in a medium, heavy saucepan; season with 1/8 teaspoon pepper. Bring to a boil. Cover; reduce heat, and simmer until rice is tender, about 45 minutes. Drain rice; discard bay leaf. Let cool completely.
Preheat oven to 450 degrees. Put garlic and lemon juice into a small heatproof bowl; set aside. Cut pomegranates in half. Remove seeds from two halves; set aside 3/4 cup seeds (reserve any remaining seeds for another use). Extract juice from remaining four halves with a citrus juicer or reamer. Strain into a small saucepan. (You should have about 1 cup juice.)
Cook pomegranate juice over medium heat until syrupy and reduced to 1/4 cup, about 10 minutes. Stir into lemon juice and garlic; let glaze cool completely.
Brush 2 teaspoons oil over bottom of a 13-by-9-inch baking dish. Season both sides of chicken with 1/2 teaspoon salt and 1/8 teaspoon pepper. Put chicken, bone side down, into prepared dish; brush all over with glaze. Roast, brushing with glaze every 8 to 10 minutes and adding 1/4 cup water each time, until an instant-read thermometer inserted into the thickest part of the chicken registers 165 degrees, 30 to 35 minutes.
Brush chicken with pan glaze. Tent dish with foil; let chicken rest 10 minutes.
Heat remaining tablespoon oil in a large nonstick skillet. Add onion, and cook, stirring occasionally, until tender and translucent, about 6 minutes. Stir in cumin, and cook 1 minute. Add rice; cook, stirring occasionally, until heated through, about 5 minutes. Stir in nuts, scallion, cilantro, pomegranate seeds, and remaining 1/4 teaspoon salt. Remove from heat. Divide rice mixture among 4 plates. Remove chicken from bone, and cut on the diagonal into 1/2-inch-thick slices. Arrange over rice, dividing evenly. Garnish with cilantro sprigs.