... a healthy option of squash he is regularly taking (5)
I believe the answer is:
sushi
'a healthy option' is the definition.
'squash he is regularly taking' is the wordplay.
'regularly taking' indicates alternate letters.
'squash'+'he'+'is'='squashheis'
The alternating letters of 'squashheis' are 'SUSHI'.
'of' is the link.
(Other definitions for sushi that I've seen before include "Japanese rice-based dish" , "Japanese cuisine" , "exotic dish" , "rice dishes" , "'Dish of rice, vegetables and raw fish (5)'" .)