Translation:You are asked to pick delicious food.
No, telah is not needed. The di prefix makes the verb passive. It's not a question of tense, it's a question of being passive, not active. So diminta means "are asked" (or "is asked" with a he/she/it subject). Telah would put it into the past tense: "you were asked", or "you have been asked".
"You are asked" means that somebody else asked you. "You asked" means that you did the asking (past tense).