Allowed to slice up eastern vegetable (7)
I believe the answer is:
lettuce
'vegetable' is the definition.
(lettuce is a kind of vegetable)
'allowed to slice up eastern' is the wordplay.
'allowed to' becomes 'let' (I've seen this in another clue).
'slice' becomes 'cut' (synonyms).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'eastern' becomes 'e'.
'cut' written backwards gives 'tuc'.
'let'+'tuc'+'e'='LETTUCE'
(Other definitions for lettuce that I've seen before include "Lamb's -; iceberg -" , "Plant for the salad bowl" , "Plant with broad crisp leaves used in salads" , "eg Webbs wonder" , "Basic salad ingredient" .)