Water-based dish from France is high level (7)
I believe the answer is:
plateau
'high level' is the definition.
(plateau can refer to a piece of high ground)
'water-based dish from france' is the wordplay.
'water' becomes 'eau' (I have seen 'French water ' mean 'eau' so perhaps 'water' could also mean 'eau').
'based' says to put letters next to each other (in a down clue, some letters are based on others).
'dish from france' becomes 'plat' ('plate' in French).
'eau' put after 'plat' is 'PLATEAU'.
'is' is the link.
(Other definitions for plateau that I've seen before include "High level land area" , "High flattish area" , "Large level tract of elevated land" , "Flat highland" , "State of little change after a period of activity" .)