Soldiers tucked into lousy food (5)
I believe the answer is:
bread
'food' is the definition.
(bread is a kind of food)
'soldiers tucked into lousy' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'tucked into' is an insertion indicator.
'lousy' becomes 'bad' ('bad' can be similar in meaning to 'lousy').
're' put within 'bad' is 'BREAD'.
(Other definitions for bread that I've seen before include "Loaf; money" , "''Eaten . . . . . is soon forgotte''" , "Nan, for instance" , "It may be made from meal" , "Gracefully thin" .)