Unsettling Scot, Alan, touring, it's well done (15)
I believe the answer is:
congratulations
'well done' is the definition.
(I've seen this before)
'unsettling scot alan touring' is the wordplay.
'unsettling' indicates anagramming the letters.
'scot'+'alan'+'touring'='scotalantouring'
'scotalantouring' anagrammed gives 'CONGRATULATIONS'.
'it's' acts as a link.
(Other definitions for congratulations that I've seen before include "praise" , "well done" , "Cliff Richard hit" , "good show" , "Best wishes" .)