Boris unsettled about temperature in restaurant (6)
I believe the answer is:
bistro
'restaurant' is the definition.
(I know that bistro is a type of restaurant)
'boris unsettled about temperature' is the wordplay.
'unsettled' indicates an anagram.
'about' means one lot of letters goes inside another.
'temperature' becomes 't' (abbreviation).
'boris' anagrammed gives 'bisro'.
'bisro' going around 't' is 'BISTRO'.
'in' acts as a link.
(Other definitions for bistro that I've seen before include "somewhere to eat" , "Small bar-cum-restaurant" , "Eating place" , "Modest restaurant" , "Small informal french-style resturaunt" .)