Innocent one seen in North Avenue (5)
I believe the answer is:
naive
'innocent' is the definition.
(similar in meaning)
'one seen in north avenue' is the wordplay.
'one' becomes 'i' (Roman numeral).
'seen in' indicates putting letters inside.
'north' becomes 'N' (abbreviation).
'avenue' becomes 'ave'.
'n'+'ave'='nave'
'i' inserted within 'nave' is 'NAIVE'.
(Other definitions for naive that I've seen before include "Simple in style or behaviour" , "Jejune" , "Simple-minded" , "Inexperienced, gullable" , "Too trusting and impractical" .)