Prepare the portabello mushrooms by washing, drying completely, removing the stems, and cut into 1/4-inch thick slices.
Add some of the breadcrumbs into a bowl for coating. Add more as needed after you start breading the mushroom slices.
In another medium bowl , combine all the ingredients for the Batter in the order listed and whisk until completely mixed.
Dredge each slice of mushroom into the batter to coat thoroughly on both sides and then into the breadcrumbs.
Place the breaded mushroom slices on the parchment lined baking sheet. Note: Keep the whisk handy so that you can quickly whisk the batter mixture when needed if you feel like the contents of the batter start to settle (this will probably happen after prepping 2-3 mushroom slices).
Once all the mushroom slices are breaded and placed in a single layer on the baking sheet, sprinkle some sea salt and freshly ground black pepper, and bake them in the oven for 20-25 minutes. Flip half way through so that they bake for 10-12 minutes on each side or until golden brown and crispy on the outside.
Enjoy them with a side of some vegan cucumber ranch or chipotle aioli .