동사 + 은/는 김에
In the following sentence, I don't understand why the 김에 tense that is used is used.
'우리 만난 김에 식사나 하자.'
My confusion is, if 하자 is a suggestion, as in an action for the future, and 은 김에 is to be used with past tense verbs, why are the used together here.
Shouldn't the 김에 form be future tense?