Heat stock, bringing to boil and then down to simmer.
Melt the butter in a large non stick skillet over medium heat. Add onions and cook for 2 minutes or until the onion is softened. Add the rice and stir to coat the rice with butter. Cook 3 minutes stirring often so that the rice does not burn.
Transfer rice to large baking dish. Pour in hot stock. Stir in lemon juice, zest, bay leaves, salt and pepper.
Cover pan tightly with aluminum foil and bake for 25-30 minutes or until all liquid is absorbed and the rice is tender.
Fluff the rice just before serving and garnish with lemon slices and sliced green onion if desired.