As an alternative, left of the nose (5)
'of the nose' is the definition.
(I've seen this before)
'as an alternative left' is the wordplay.
'alternative' indicates anagramming the letters.
'left' becomes 'l' (common abbreviation).
'asan' anagrammed gives 'nasa'.
(Other definitions for nasal that I've seen before include "Part of helmet", "Describing some hooter", "Hooters", "Pertaining to the nose", "Like sounds of m, n, ng".)