Pat lamb dry with paper towel and place on a plate. Mix hoisin, sugar and sesame oil in a bowl with 1 tablespoon warm water until smooth. Brush marinade onto lamb.
Preheat a chargrill pan over high heat until very hot. Place a piece of baking paper on the grill to prevent sticking and place lamb chops on the baking paper. Cook in batches to prevent overcrowding. Cook lamb for 4-5 minutes each side until marks appear and lamb is cooked to medium. Rest for 5 minutes.
Wash choy sum and toss with capsicum and broccolini in a hot frying pan or wok for 1 minute. Drizzle with a little sesame oil and hoisin sauce.
Serve lamb with vegetables and steamed brown rice.
You can marinate the lamb overnight if you have time for extra tenderness.