This is a poetic Birkat haMazon for Pesaḥ, from the Cairo Geniza (CUL T-S H11.88 1v). Much thanks to the work of Dr. Avi Shmidman, whose 2009 doctoral thesis is the foundational work for poetic Birkat haMazon studies. He marks it as Piyyut 64, and his Hebrew-language commentary begins on page 394 of his work. I’ve included two translations of the poetic portions — one literal and one preserving the acrostic and rhyme scheme.