A can-opener cuts open ham (7)
I believe the answer is:
overact
'ham' is the definition.
('overact' can be a synonym of 'ham')
'a can-opener cuts open' is the wordplay.
'opener' suggests taking the first letters.
'cuts' indicates putting letters inside (some letters cut their way into other letters).
'open' becomes 'overt' ('overt' is associated in meaning with 'open'**).
The initial letter of 'can' is 'c'.
'a'+'c'='ac'
'ac' going inside 'overt' is 'OVERACT'.
(Other definitions for overact that I've seen before include "Be unsubtle on stage" , "pile it on" , "Exaggerate" , "Be excessive on stage" , "Be excessive like fulsome thespian" .)