Spots Her Majesty having a bit of bacon (6)
I believe the answer is:
rasher
'a bit of bacon' is the definition.
(I've seen this before)
'spots her majesty' is the wordplay.
'spots' becomes 'rash' (I've seen this before).
'her majesty' becomes 'er' (Elizabeth Regina).
'rash'+'er'='RASHER'
'having' is the link.
(Other definitions for rasher that I've seen before include "A tasty slice of bacon" , "American fish" , "More wildly adventurous" , "Tasty strip of bacon" , "More impetuous - slice of meat" .)