Boil these bananas with energy (6)
I believe the answer is:
seethe
'boil' is the definition.
(I know that seethe is a kind of boil)
'these bananas with energy' is the wordplay.
'bananas with' is an anagram indicator (informal term for mad).
'energy' becomes 'e' (physics symbol as in E=mc2).
'these' anagrammed with 'e' can make 'SEETHE'.
(Other definitions for seethe that I've seen before include "(Of liquid) boil" , "Simmer with anger" , "get very angry" , "exhibit anger" , "Boil or become very angry" .)