To slice the onions, I highly recommend using a mandolin to slice them as thin as possible. If you have a sharp knife and are good with it you can try that too. Either way, slice them as thin as possible.
Next, roll up 2 - 3 ounces (55 - 85G) of the plant based meat into balls. 3 oz will get your 4 burgers, 2 will get you 6!
Get a well seasoned cast iron or carbon steel skillet preheated over medium high heat. You can also use a non-stick pan, but don't overheat it, I would suggest heating it on medium.
I like to dry toast my buns as the pan preheats, once they are lightly toasted, it's a good sign the pan is hot enough for the burgers.
Once pan is preheated (after about 3-4 minutes) add a ball of meat to the center. Season with salt or pepper (I like to use Lawry's Seasoned Salt). Then add about 1 - 2 ounces of the sliced onions. Season some more, then smash with a burger press or stiff spatula.
Cook for 1 - 2 minutes or until you can see a nice layer of browning around the edge of the patty. Some of the onions will likely hang down and lay on the pan. If they are getting browned that is a good sign to flip too.
The burger will be stuck to the pan more than likely. Using a stiff metal spatula or scraper, scrape the burger patty around the edges, making sure not to tear up the crust. Once it releases from the pan, flip it over. Cook for a minute or so, then add some vegan cheese. Drizzle in a little water and cover to steam and melt the cheese.
Add to the buns, dress with any condiments and pickles that you like and enjoy!