Reckless monarch starting to slice some bacon (7)
I believe the answer is:
rashers
'some bacon' is the definition.
(as in rashers of bacon)
'reckless monarch starting to slice' is the wordplay.
'reckless' becomes 'rash' (synonyms).
'monarch' becomes 'ER' (abbreviation for Elizabeth Regina, British Queen).
'starting to' suggests taking the first letters.
The initial letter of 'slice' is 's'.
'rash'+'er'+'s'='RASHERS'
(Other definitions for rashers that I've seen before include "Thin slices of bacon" , "Meat slices" , "Tasty strips of bacon" , "eaten at breakfast" .)