Wash and slice the portobello mushrooms about 1/4 inch in thickness.
Pour 2 tablespoons of oil onto a metal baking sheet along with 2 teaspoons of liquid smoke, 1 teaspoon of liquid aminos (or soy sauce), and a sprinkle of salt. Stir it up and spread it around the bottom of the pan evenly.
Place the sliced mushrooms on top of the marinade, allow them to sit for a minute or two to soak up some of the liquid, then flip them over. Sprinkle with a little more salt (about 1/4 tsp.)
Place them in the oven at 375° F (190° C)and bake for 15 minutes. Then take the tray out of the oven and flip each mushroom over.
Bake again for another 15 minutes, then flip them one more time. Bake for another 5-10 minutes until they are rubbery.
Take them out of the oven and allow them to cool on the tray for about 15 minutes. (They will continue to dehydrate a little more while they are cooking.)
Wipe off any excess oil with a paper towel. Store them in a glass jar or a plastic bag in a cool, dry place or in the fridge if you won't be eating them in the next few days.
Notes
If you are going to be leaving them out of refrigeration for a long period of time, be sure to bake them until all of the liquid is out of the mushrooms.
Watch the mushrooms closely towards the end of baking; they can go from crispy to burnt very quickly.
It seems like a lot of mushrooms to start, but the mushrooms will shrink a lot in the dehydration process.