Part of Mexico coast ruined with a British incursion (7)
I believe the answer is:
tabasco
'part of mexico' is the definition.
(I know that Tabasco is part of Mexico)
'coast ruined with a british incursion' is the wordplay.
'ruined' indicates an anagram.
'with' indicates putting letters inside.
'a british incursion' becomes 'ab' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'coast' is an anagram of 'tasco'.
'tasco' going around 'ab' is 'TABASCO'.
Can you help me to learn more?
(Other definitions for tabasco that I've seen before include "Hot pepper sauce" , "Hot peppery sauce" , "Hot sauce made from capsicums" , "Mexican state; pungent sauce" , "Mexico state" .)