In a small bowl, mix chili sauce, oyster sauce, lemon juice, and cilantro.
To shuck each oyster, place shell, cupped side down, on a heavy towel. Grip curved end of shell with a towel and hold oyster level. Firmly insert an oyster knife into hinge at narrow end of oyster between top and bottom shell; twist to open. Slide oyster knife along underside of top shell to cut adductor muscle and free oyster. Remove top shell. Slide knife under oyster to cut free. Leave in shell and set shell side down on a tray.
Spoon an equal portion of the chili sauce mixture onto each oyster.
Set oysters on a barbecue grill over a solid bed of hot coals or high heat on a gas grill (you can hold hand at grill level only 2 to 3 seconds); close lid on gas grill. Cook until juices bubble, about 4 minutes.
Serve hot oysters in shells.