What's more in Belgium, Germany is in view on the way back (7)
I believe the answer is:
besides
'what's more' is the definition.
(I've seen this before)
'belgium germany is in view on the way back' is the wordplay.
'belgium' becomes 'B' (international vehicle registration code).
'germany' becomes 'd' (vehicle registration code for Deutschland).
'in' is an insertion indicator.
'view' becomes 'see' (synonyms).
'on the way back' shows that the letters should be reversed in order.
'd'+'is'='dis'
'dis' placed within 'see' is 'sedise'.
'sedise' back-to-front is 'esides'.
'b'+'esides'='BESIDES'
'in' acts as a link.
(Other definitions for besides that I've seen before include "What's more" , "Moreover" , "to boot" , "In addition, as well" , "also is available" .)