In new diet, flavour finally tasted (5)
I believe the answer is:
tried
'tasted' is the definition.
('try' can be a synonym of 'taste')
'in new diet flavour finally' is the wordplay.
'in' means one lot of letters goes inside another.
'new' indicates an anagram.
'finally' suggests the final letters.
The final letter of 'flavour' is 'r'.
'diet' is an anagram of 'tied'.
'tied' placed around 'r' is 'TRIED'.
(Other definitions for tried that I've seen before include "heard in court" , "Attempted" , "Endeavoured" , "Essayed" , "Had a crack" .)