Wash hens, pat dry. Chop giblets. In skillet, sauté onion in oil. Add giblets. sauté 4 minutes. Add spinach, salt, thyme, and pepper. Cook 5 minutes, stirring often. Remove from heat. Add rice, cheese, 1/4 cup white wine, and Marsala. Spoon into hens. Fold back wings and tie legs. Place on rack in shallow pan. Cover loosely with foil. Bake 30 minutes at 350 degrees F. Uncover. Blend remaining cup of white wine with lemon juice, butter, and tarragon. Spoon over hens. Bake 30 minutes more or until done, basting occasionally. Serve with marinade from pan.