Good job it's thoroughly cooked! (4,4)
I believe the answer is:
well done
This clue is a double definition.
'good job' is the first definition.
(both might be said to acknowledge an achievement)
'thoroughly cooked' is the second definition.
(I've seen this before)
'it's' is the link.
(Other definitions for well done that I've seen before include "how you might get the chop" , "Words of praise" , "how a steak may have been cooked" , "By no means rare" , "Congratulations - cooked right through" .)