It should be “piece” as in “piece of my mind”, ie your opinion.
Found a source:
‘Say your piece and hold your peace are separate idioms. "Say your piece" refers to stating your opinion, or your "piece" or "part" of the conversation. This is often confused with "hold your peace," which is often associated with marriage objections and refers to remaining silent and peaceful. Frequently, even in professional writing, the confusion is apparent and written as "say your peace."’
You are presumably confusing that phrase with the old-timey "speak now or forever hold your peace", which is using the term "peace" in the same sense one might speak of a "justice of the peace;" i.e. civil peace. In a society where people are no longer subject to threats of physical violence or death for bigamous, morganatic, or religiously impure weddings, it has lost all relevant meaning and is just an archaicism.
On an even more boring subject, does one say their piece or say their peace?
It should be “piece” as in “piece of my mind”, ie your opinion.
Found a source:
‘Say your piece and hold your peace are separate idioms. "Say your piece" refers to stating your opinion, or your "piece" or "part" of the conversation. This is often confused with "hold your peace," which is often associated with marriage objections and refers to remaining silent and peaceful. Frequently, even in professional writing, the confusion is apparent and written as "say your peace."’
https://www.merriam-webster.com/grammar/say-your-piece-versus-peace-usage
Piece.
You are presumably confusing that phrase with the old-timey "speak now or forever hold your peace", which is using the term "peace" in the same sense one might speak of a "justice of the peace;" i.e. civil peace. In a society where people are no longer subject to threats of physical violence or death for bigamous, morganatic, or religiously impure weddings, it has lost all relevant meaning and is just an archaicism.