Finished a lasagne? (5)
I believe the answer is:
pasta
'lasagne?' is the definition.
(lasagne is a kind of pasta)
'finished a' is the wordplay.
'finished' becomes 'past'.
'past'+'a'='PASTA'
(Other definitions for pasta that I've seen before include "Staple food of Italy" , "tagliatelle perhaps" , "The stuff of spaghetti, macaroni etc" , "Processed flour dough" , "dish of food" .)