Food that's regularly vegan? Tosh! (4)
I believe the answer is:
eats
'food' is the definition.
(eats is a kind of food)
'regularly vegan? tosh' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'vegan'+'tosh'='vegantosh'
The alternate letters of 'vegantosh' are 'EATS'.
'that's' is the link.
(Other definitions for eats that I've seen before include "Victuals" , "meal" , "Chews" , "Takes meals" , "Scoff" .)