I have been making these at New Years Eve for over 40 years.
My Mom would make them when we were kids, when my great aunt Ethel and uncle Bob would come over to watch Lawrence Welk and play penny any poker, I call them spamburgers and they are great.
try adding a small clove of garlic to the mix and cook them until the bun just starts to get toasty and crisp, yummy.
Many fond memories.

I also add 2 diced eggs and some cocktail sauce to the mix. They freeze well before baking.

My granny used to make these for us in the 60's. She'd use her manual meat grinder and just put every thing through it into a bowl, then added a dollop of Miracle Whip and broil them open faced on hamburger buns. So freakin' good!