It's natural I see when eye, say, opens (7)
I believe the answer is:
organic
'it's natural' is the definition.
(similar in meaning)
'eye say opens' is the wordplay.
'eye say' becomes 'organ' (eye is a kind of organ).
'opens' becomes 'ic' (I am not sure about this - if you are sure you should believe this answer much more).
'organ'+'ic'='ORGANIC'
'i see when' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for organic that I've seen before include "In cargo (anag.)" , "Chemical and GM free" , "No cigar (anag.)" , "Made from living matter" , "Derived from animal or vegetable matter" .)