兩邊俱熟 Done On Both Sides Through
八戒道：「哥啊，依你說，就活活的弄殺人了。他打緊見不上氣，擡開了，把我翻轉過來，再燒起火，弄得我兩邊俱熟，中間不夾生了？」八戒道：「哥啊，依你说，就活活的弄杀人了。他打紧见不上气，抬开了，把我翻转过来，再烧起火，弄得我两边俱熟，中间不夹生了？」
逐句解 Line by line
Bajie said, "Brother, by your account they are going to kill me by inches.
活活的弄殺人, to do a man to death while he is still alive, is Bajie's usual register: physically vivid and grammatically excessive. There is no calmer way to say it that keeps the flavour.
The moment he sees the steam is not coming up he will lift the tray off, turn me over, build the fire up again, and have me done on both sides with the middle still raw!"
This is the punchline and it is a cook's punchline. 夾生, half-raw in the middle, is the exact word for food cooked at the outside and uncooked within, and any Chinese kitchen still uses it. 中 is zhōng, the middle. Bajie has followed Wukong's lecture perfectly and worked out the consequence for himself.
Bajie proves he was paying attention, and the proof takes the form of the worst possible conclusion. If the steam does not come up, the cook will do the obvious thing, and the obvious thing is worse than being cooked properly.
The word he lands on is the one that makes the joke land. Half-raw in the middle is a complaint about a dumpling, and he is applying it to himself. Grand horror would be easier to shrug off; being badly cooked is a humiliation anybody who has eaten a bad meal can picture.
It is also the first time in the chapter that Wukong's competence has made someone feel worse. The lecture was meant to be reassuring — the enemy is an amateur, so we are safe — and Bajie has correctly worked out that an incompetent cook is in some ways a more frightening prospect than a good one.