Healthy meal as rejected by young fellow (5)
I believe the answer is:
salad
'healthy meal' is the definition.
(I've seen this in another clue)
'as rejected by young fellow' is the wordplay.
'rejected' is a reversal indicator.
'by' means one lot of letters go next to another.
'young fellow' becomes 'lad' (lad can mean a young boy).
'as' back-to-front is 'sa'.
'sa'+'lad'='SALAD'
(Other definitions for salad that I've seen before include "One may well be green" , "Lettuce, cucumber etc" , "rabbit food" , "Raw, green, veg" , "Green, potato, Russian or Waldorf?" .)