Spice copper starts mixing into nachos? (5)
I believe the answer is:
cumin
'spice' is the definition.
(cumin is a spice)
'copper starts mixing into nachos?' is the wordplay.
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'starts' suggests taking the first letters.
The first letters of 'mixing into nachos' is 'min'.
'cu'+'min'='CUMIN'
(Other definitions for cumin that I've seen before include "Curry powder ingredient" , "Aromatic (curry) spice" , "Spice used in curries" , "relief from wind" , "Curry-seasoning herb" .)