Lament about occasionally mealie vegetable (6)
I believe the answer is:
celery
'vegetable' is the definition.
(I know that Celery is a type of vegetable)
'lament about occasionally mealie' is the wordplay.
'lament' becomes 'cry' (I've seen this in another clue).
'about' indicates putting letters inside.
'occasionally' means one should take alternating letters.
The alternate letters of 'mealie' are 'ele'.
'cry' enclosing 'ele' is 'CELERY'.
(Other definitions for celery that I've seen before include "Plant with edible stalks" , "Plant with edible stems" , "Aromatic leaf stalks, raw or cooked" , "Edible leaf stalks" , "Vegetable with crisp stalks" .)