Combine lemongrass, ginger, brown sugar, rice vinegar, black pepper, soy sauce, and fish sauce in a bowl. Pierce pork chops using a fork and add the marinade. Turn to coat and let marinate for at least 30 minutes or up to 3 hours.
Preheat the broiler over high heat and broil the pork (discard the marinade) until brown and cook through.
Serve over rice with Nuoc Cham (Vietnamese chili-garlic sauce) and garnish with green onions.