Seafood and soy mixed by the Irish regularly (7)
I believe the answer is:
oysters
'seafood' is the definition.
(I know that oysters is a type of seafood)
'soy mixed by the irish regularly' is the wordplay.
'mixed' is an anagram indicator.
'by' says to put letters next to each other.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'the'+'irish'='theirish'
The alternating letters of 'theirish' are 'ters'.
'soy' is an anagram of 'oys'.
'oys'+'ters'='OYSTERS'
'and' acts as a link.
(Other definitions for oysters that I've seen before include "Yet Ross can find the marine creatures" , "Tasty bivalves, may contain pearls" , "Rosy set of odd shellfish" , "Tasty pearl-producing bivalves" , "Fleshy bivalves, may yield pearls" .)