Old containers in the kitchen holding last of grilled mushrooms (7)
I believe the answer is:
expands
'mushrooms' is the definition.
(mushroom can mean to expand or swell)
'old containers in the kitchen holding last of grilled' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'containers in the kitchen' becomes 'pans' (I can't justify this - if you can you should believe this answer much more).
'holding' means one lot of letters goes inside another.
'last of' indicates one should take the final letters.
The last letter of 'grilled' is 'd'.
'pans' enclosing 'd' is 'pands'.
'ex'+'pands'='EXPANDS'
Can you help me to learn more?
(Other definitions for expands that I've seen before include "Becomes larger" , "gets bigger" , "Enlarges" .)