아침먹었냐?   Did you have a breakfast?
점심먹었냐?  Did you have a lunch?
저녁먹었냐?   Did you have a dinner?
저녁이나 같이 먹자  Let's have a dinner.
밥이나 같이 먹자  Let's have a meal.

정중하게 밥을 같이 먹자고 할때는  Would you like to have a meal together? or
 Do you have a time? I 'd like to  have a dinner with you.