...got my arse handed to me on a plate.
Pretty certain it is indeed an Americanism. An (awkward?) combination of "getting your arse handed to you" as in you got your butt kicked so badly in a fair fight it came off and the folks that did the kicking needed to give it back to you, and "on a plate" or sometimes "on a silver platter" is an indication that essentially no real work was required to accomplish it thus throwing further shade on the recipient.
But...
The problem is that the two don't really belong together. Getting something handed to you on a plate, silver platter, with a golden spoon, etc. is a phrase meant to belittle the recipient as in "being the spoiled brat they are they grew up expecting everything to being given to them rather than having to actually work to achieve it."
I suspect the combination was put together because a fellow Yank thought it sounded cool without really understanding what they were doing. This abuse of the language is similar to that which sees folks who attended an orientation briefing to be "orientated" rather than "oriented" and folks saying "I could care less about (whatever)" rather than "I couldn't care less."
A great oversimplification comes from a quote by that great Spanish philosopher, Professor I. Montoya, who so eloquently put it:
"You keep using that word. I do not think it means what you think it means."