Guilt-free bacon, essentially without fat (5)
I believe the answer is:
clean
'guilt-free' is the definition.
(clean can mean guilt-free or legal)
'bacon essentially without fat' is the wordplay.
'essentially' means to look at the middle letters.
'without fat' becomes 'lean' (I've seen this in another clue).
The middle letter of 'bacon' is 'c'.
'c'+'lean'='CLEAN'
(Other definitions for clean that I've seen before include "Pure; well-defined" , "Completely (colloq.), free of dirt" , "Not soiled, free from dirt" , "Devoid of dirt" , "Not dirty" .)