Plenty are an awkward shape (5)
I believe the answer is:
heaps
'plenty' is the definition.
(I've seen this in another clue)
'an awkward shape' is the wordplay.
'an awkward' indicates an anagram.
'shape' anagrammed gives 'HEAPS'.
'are' acts as a link.
(Other definitions for heaps that I've seen before include "Mounds; lots" , "A large number; untidy mounds" , "Mounds, stacks" , "Shape (anag) - lots" , "Lots (of piles?)" .)