"Juicy whole chicken roasted or cooked on a rotisserie. It remains a popular street food in the Philippines. It's best to give it time to marinate so that the flavors meld together. Serve it with Nina's Lechon Sauce."
Combine onion, garlic, calamansi juice, fish sauce, salt, black pepper, and brown sugar in a bowl to make marinade.
Place chicken in a roasting pan. Rub marinade over chicken, including inside the cavity. Let chicken marinate in the refrigerator, about 4 hours. Reserve leftover marinade in the bowl.
Preheat oven to 400 degrees F (200 degrees C).
Trim lemongrass, discarding tough outer stalks. Pound inner stalks with a heavy object until bruised. Place lemongrass and bay leaves inside the chicken cavity.
Stir oil into the leftover marinade in the bowl.
Roast chicken in the preheated oven, basting with the oil mixture from time to time, until an instant-read thermometer inserted into the thickest part of the thigh reads 165 degrees F (74 degrees C), 60 to 90 minutes.
Remove chicken from the oven and allow to rest in a warm area for 15 minutes before serving.