What to have at Chinese restaurant? It’s no great intellectual problem (3,3)
I believe the answer is:
dim sum
'what to have at chinese restaurant?' is the definition.
'no great intellectual problem' is the wordplay.
'no great intellectual' becomes 'dim'.
'problem' becomes 'sum' (arithmetic problem).
'dim'+'sum'='DIM SUM'
'it's' is the link.
(Other definitions for dim sum that I've seen before include "Chinese fare" , "Failure of mathematician, possibly" , "Asian food" , "fare from China" , "oriental dish" .)