Grind the fennel, cumin, turmeric, and chili flakes in a coffee grinder. In a food processor, pulverize the ground spices, cilantro, scallions, lemongrass, garlic, and ginger. Add oyster sauce and coconut milk, and season with salt to taste.
Rub the mixture on the inside and outside of the chicken. Let chicken marinate in the refrigerator for 2 to 3 hours. Preheat oven to 300 degrees F. Place chicken on a rack in a large roasting pan, and roast for 2 hours or until done. Let rest, for 10 minutes before carving.
Serve on a bed of seasoned rice with Pepper-Papaya-Pineapple Chutney.