Use a damp towel to gently clean the mushrooms. Trim off the coarse part of the stems (soft stems are ok), and place the mushrooms in a medium bowl. Drizzle with olive oil, rice vinegar and sprinkle with a pinch of salt. Gently toss and aside to marinate.
Preheat the oven to 450 °F and line a baking sheet with parchment paper.
In a small bowl, stir the ground flaxseed together with the water.
In a small bowl, combine the cornmeal, panko, hemp seeds, Old Bay, cayenne, and a few pinches of salt and pepper. Pour the breading mixture onto a plate.
Bread the mushrooms by dipping each one into the flax mixture, let some of the excess drip off, then place it onto the breading plate and gently coat the mushroom with the breading. Repeat for all mushrooms. Once you get toward the end, if you’re running out of flax, or if you have smaller pieces of mushrooms, scrape the remaining flax in the mushroom bowl, toss, then add in the remaining breading and toss to coat.
Bake for 10-12 minutes or until golden brown and crisp on the edges. Remove from the oven and squeeze fresh lemon juice onto the mushrooms.
Assemble sandwiches, filling buns with Dijonnaise, arugula, tomato slices, and pickles. Serve with lemon wedges on the side.
if you don't have Old Bay Seasoning, substitute it with a combination of smoked paprika, onion powder, black pepper, and celery salt.
Recipe by Love and Lemons at https://www.loveandlemons.com/oyster-mushroom-po-boys/