using polenta to make hamburger
I don't think you're going to get a good ground beef substitute from polenta, for that I would recommend TVP or other vegan soy crumbles, seitan or even mushrooms. However, if you're interested in making a veggie burger out of polenta, I'm sure you could look online for a recipe (for example here, but you may find others). It's certainly not going to taste anything remotely like beef, though.