After about twice touring one, fix Middle East vault (5,4)
I believe the answer is:
onion dome
'vault' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'after about twice touring one fix middle east' is the wordplay.
'after about twice touring one' becomes 'onion' (I can't justify this - if you can you should believe this answer much more).
'fix' becomes 'do' (I've seen this in other clues).
'middle east' becomes 'me' (abbreviation for Middle East).
'onion'+'do'+'me'='ONION DOME'
Can you help me to learn more?
(Other definitions for onion dome that I've seen before include "Roof feature such as on Brighton Pavilion" , "Byzantine structure?" , "Roof shaped like a pungent vegetable, on a Russian church, perhaps" , "part of Russian church?" , "Feature of eastern churches" .)