what do you usually have for lunch?和 what do you usually hav

我怎么觉得第二句语法不通呀,如果问通常中午吃什么应该是what do you usually have for lunch, 如果去掉那个for就可以问在那吃,where do you usually have lunch
说你语法错就是因为问午饭吃什么就应该是for lunch,中间要加个介词,如果不加就要换意思了,如果不加可以改成我后面说的那句,问在哪吃,或者别的.