S. American chain regularly offering rice-based dish (5)
I believe the answer is:
sushi
'dish' is the definition.
(I know that sushi is a type of dish)
's american chain regularly' is the wordplay.
'american' becomes 'US' (United States).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'chain' are 'hi'.
's'+'us'+'hi'='SUSHI'
'offering rice-based' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sushi that I've seen before include "Asian dish" , "Japanese food" , "Cold rice balls with raw fish" , "Japanese cold rice dish" , "cold food" .)