Occupy one zone within religious district (5)
I believe the answer is:
seize
'occupy' is the definition.
(thesaurus)
'one zone within religious district' is the wordplay.
'one' becomes 'i' (Roman numeral).
'zone' becomes 'z'.
'within' is an insertion indicator.
'religious district' becomes 'see' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'i'+'z'='iz'
'iz' placed within 'see' is 'SEIZE'.
Can you help me to learn more?
(Other definitions for seize that I've seen before include "Clutch" , "Grasp hold of" , "Impound" , "Get hold of" , "Take hold of, grab" .)