晚餐要吃飽
Be sure to have a full meal at dinner.
[update]
Be sure to have your fill at dinner.
Be sure to eat as much as you desire at dinner.
eat one's fill 是舊式用法 (old-fashioned),很少聽人這麼說。
have/get one's fill 可以表達"要吃飽"的意思
https://idioms.thefreedictionary.com/get+one%27s+fill