My idea of an ultimate burger is one that has all of the fixin's I like. So it be the same with you..but you get the paleo picture. No bun! And you don't miss it with flavors like this.
1 portabello cap
4 ounces ground grass fed beef
salt and pepper
1 ounce sliced raw cheese
1 slice onion
1 slice tomato
1/4 avoccado, sliced
Coat portabello cap with olive oil. Heat grill pan over medium high heat. Add cap and cook until soft and tender, about 5-7 minutes depending on the size of the cap. Remove and set aside.
Add salt and pepper, generously to the meat, and then form into a patty. Indent the center slightly so that the patty cooks evenly. Add to grill pan and place the onion in the pan as well. Cook to your doneness, but I will say that beef should only be eaten, in my humble opinion, medium rare. Cook onion so that it is translucent and both sides are caramelized.
When they are finished, place portabello on a plate, and then stack. Enjoy!