Expressionless dish that has passed away (7)
I believe the answer is:
deadpan
'expressionless dish that has passed away' is the definition.
'deadpan' can be an answer for 'expressionless' (I've seen this before). I am not sure about the remainder of the definition.
'expressionless dish' is the wordplay.
'expressionless' becomes 'dead' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'dish' becomes 'pan' (I have seen 'Shallow dish ' mean 'pan' so perhaps 'dish' could also mean 'pan').
'dead'+'pan'='DEADPAN'
Can you help me to learn more?
(Other definitions for deadpan that I've seen before include "Serious-looking" , "without a flicker" , "Poker-faced" , "Impassive" , "Lifeless" .)