Yes, the meat grinder. Because, why not?
I'd never tried putting cooked meat through the meat grinder, so that was good enough reason.
I figured it needed some binder, so I added egg and I thought mustard would be a nice flavor, so I put in a dollop of grainy mustard. I probably should have added some bread or cracker crumbs, but I didn't,
I had enough to make 4 burger-sized patties. I put them in a nonstick pan with a little oil and let them brown well on one side. They were still a little soft and a bit tricky to flip, but they didn't fall apart. After the second side was browned, they held together a lot better.
The texture wasn't like a burger, it was more like salmon patties. And the color was a similar pink. They got a nice brown crust, which was nice.
If I make them again, I'll probably add some bread or cracker crumbs so they bind better, and maybe some chopped onion or scallions. The mustard way a nice touch, so I'll keep that.