In a large resealable plastic bag or a non-metal baking dish, combine the onion, soup mix, oil, and juice. Add the chicken, turning to coat evenly. Marinate in the refrigerator for 2 hours. Heat the oven to 350 degrees. Transfer the chicken and marinade to a 13x9-inch baking or roasting pan or leave in the baking dish. Bake the chicken, uncovered, basting occasionally, 40 minutes or until done.