Upending old tin containing hot Mexican food (5)
I believe the answer is:
nacho
'mexican food' is the definition.
(I've seen this before)
'upending old tin containing hot' is the wordplay.
'upending' is a reversal indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tin' becomes 'can' (synonyms).
'containing' means one lot of letters goes inside another.
'hot' becomes 'h' (abbreviation eg on taps).
'o'+'can'='ocan'
'ocan' placed around 'h' is 'ohcan'.
'ohcan' back-to-front is 'NACHO'.
(Other definitions for nacho that I've seen before include "chip production line unit" , "Tortilla crisp" , "Small piece of tortilla with a topping" , "Mexican food item" , "part of a snack?" .)