To make the marinade, use a food processor to blend garlic, ginger, lemongrass, salt, kalamansi juice, vinegar, annatto oil, and black pepper into a paste. prepare the spatchcock chicken by cutting the spine and slicing the bone between the breasts. pour the marinade onto the chicken and marinate for 2 hours or overnight. cook the chicken in an oven tray at 180c for 1 hour, then finish on a grill or bbq, basting each side until golden brown.