Marmite regularly seen around in France: well, that's relaxing (7)
'relaxing' is the definition.
(e.g. ambient music)
'marmite regularly seen around in france well' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'seen around' indicates putting letters inside.
'in france well' becomes 'bien' (French for 'well').
The alternate letters of 'marmite' are 'amt'.
'amt' placed around 'bien' is 'AMBIENT'.
'that's' is the link.
(Other definitions for ambient that I've seen before include "Surrounding - mean bit (anag)", "Surrounding, temperature perhaps", "Related to the immediate surroundings", "sort of music", "Going around".)