Or inform one the tin is designed to hold pasta (10)
I believe the answer is:
tortellini
'pasta' is the definition.
(I know that tortellini is a type of pasta)
'or inform one the tin is designed to hold' is the wordplay.
'inform' becomes 'tell' (telling is a kind of informing).
'one' becomes 'i' (Roman numeral).
'is designed' indicates anagramming the letters (a new design of the same letters).
'to hold' means one lot of letters goes inside another.
'tin' with letters rearranged gives 'tni'.
'or'+'tell'+'i'='ortelli'
'ortelli' placed into 'tni' is 'TORTELLINI'.
(Other definitions for tortellini that I've seen before include "Small filled pasta cases" , "Pasta is called for" , "Rings for food" , "Italian dish" , "pasta dish" .)