Mixture of hot and cold on a chip (5)
I believe the answer is:
nacho
'chip' is the definition.
(I've seen this before)
'mixture of hot and cold on a' is the wordplay.
'mixture of' indicates anagramming the letters (I've seen this in other clues).
'hot' becomes 'h' (abbreviation eg on taps).
'and' means one lot of letters go next to another.
'cold' becomes 'c' (eg on taps).
'h'+'c'+'on'+'a'='hcona'
'hcona' with letters rearranged gives 'NACHO'.
(Other definitions for nacho that I've seen before include "Tortilla crisp" , "kind of chip" , "Mexican bite" , "Small piece of tortilla with a topping" , "Piece of tortilla served with sauce" .)