Cut the stem out of the Mushrooms, and make sure they are flat-ish. If they have a large curve on the edge. Trim some of the edge so they are flat.
Then whisk together the almond milk and apple cider vinegar. Let sit for a few minutes until it begins to curdle, making vegan buttermilk.
Next, In a medium sized mixing bowl, combine the flour, corn starch, salt,garlic and pepper. Then pour the vegan "buttermilk" into the dry mixture. Whisk until fully combined and lump free.
Now, begin heating the oil on medium high in a large skillet. You want about 1/2 an inch of oil in the pan. Once the oil is hot, dip a mushroom into the batter. Coating completely.
Then, gently place into the hot oil. Fry on one side until it is nice and brown, it will take 2-3 minutes. Then flip the mushroom and fry on the other side for a few more minutes until the whole mushroom is brown and crispy.
Repeat this process with all the mushrooms. Place them on a paper towel and sprinkle with a little more salt.
Make the mayo, by whisking together the vegan mayo, agave and hot sauce.
Put together the sandwiches. A little mayo on a bun, then mushroom, cabbage or greens, then more mayo. Serve immediately!