Frame that supports way over lake in part of forest (7)
I believe the answer is:
trestle
'frame that supports way' is the definition.
'trestle' can be an answer for 'frame' (trestle is a kind of frame). I'm not certain of the rest of the definition.
'over lake in part of forest' is the wordplay.
'over lake' becomes 'stl' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'part of forest' becomes 'tree'.
'stl' placed inside 'tree' is 'TRESTLE'.
Can you help me to learn more?
(Other definitions for trestle that I've seen before include "Supporting structure for bridge or tabletop" , "Braced framework" , "Framework for holding a tabletop" , "Supporting framework for, eg, table top" , "Supporting tower" .)