Let's eat lunch.
Let's have lunch.
Why don't we go out for dinner?
ご飯食べに行こうよ。
Let's have dinner.
Let's have dinner.
I shall go to eat dinner.
Let's have lunch.
Let's eat lunch.
Let's have dinner.
Let's have lunch.
I'll treat you to dinner.
I'll go out for lunch.
I'll treat you to dinner.
We will go out to eat lunch.