Mushy peas served with pork pie, right for trainer (8)
I believe the answer is:
espalier
'trainer' is the definition.
(frame for training a plant)
'mushy peas served with pork pie right' is the wordplay.
'mushy' is an anagram indicator (letters mushed up).
'served with' means one lot of letters go next to another.
'pork pie' becomes 'lie' (I've seen this before).
'right' becomes 'r' (common abbreviation).
'peas' with letters rearranged gives 'espa'.
'espa'+'lie'+'r'='ESPALIER'
'for' acts as a link.
(Other definitions for espalier that I've seen before include "Fruit tree that grows flat against the wall" , "garden frame" , "Lattice for growing plants" , "Trellis to train plants to grow flat" , "Trellis for training fruit trees" .)