Supply seafood without container (7)
I believe the answer is:
Here is my best explanation:
'supply' is the definition.
(furnishing is a kind of supplying)
'seafood without container' is the subsidiary indication.
'seafood' becomes 'fish' (fish is a kind of seafood).
'without' is an insertion indicator.
'container' becomes 'urn' (urn is a kind of container**).
'fish' going around 'urn' is 'furnish'.
(Other definitions for furnish that I've seen before include "To supply", "Provide, supply", "Supply with table and chairs etc", "pianist's partner", "Fit out with chairs etc." and "Equip".)