Do you want to have a lunch，对吗

对的，就是费了点。
Do you want a lunch?口语中都可以的。

不对。正确用法：
have supper/breakfast/lunch/dinner/a meal
have a big supper/a quick dinner/an awful lunch/a terrible breakfast

最地道的说法:
1.Do you have lunch plan? / If not yet, do you mind join me or us?
2.Are you free for lunch?

语法上没有什么问题，只是少个问号。
但鄙人认为用Would you like to……能好一些！谢谢！

不对 = =！
不要加a

Do you want to have lunch?

what would like for lunch?会好一些 当然你那个去掉a也可以啦