Preheat oven 200c (fan) / 375f convection or 400f bake.
Trim the ‘hay’/stem from the bottom of the mushroom, keeping it all intact in one piece.
Get cast-iron pan hot and heat up 2 tbsp oil and swirl to evenly coat. Place mushrooms stem side down, into the pan on the outer edge hot spots.
Press mushrooms with another cast-iron pan/heavy pot. Apply a little pressure until you hear the sizzle. Lift top pan, wipe off the liquid with a towel, set to the side. Mushrooms will be releasing liquid, leave the water to evaporate for a couple of minutes.
Add beer to BBQ sauce in a bowl. Season mushrooms with BBQ blend seasoning (Derek & Chad used Wicked Kitchen's Hot & Spicy BBQ Rub), black pepper, granulated garlic, salt, and a 1 ½ tbsp oil. Flip mushrooms carefully with tongs.
Repeat the pressing step again and leave to cook for a few more minutes. Season mushrooms again with bbq seasoning, granulated garlic, black pepper, and salt.
Add a little oil around the edge of the pan and swirl, to prevent sticking, then flip mushrooms carefully again. Turn mushrooms again until charred and crispy on both sides, then place gently into the bowl of BBQ sauce, push down with hands until mushrooms are completely coated.
Place saucy mushrooms onto a parchment-lined baking sheet and add a little more BBQ sauce to the top of each mushroom.
Cook in the oven for 10-15 minutes. Remove and serve on a chopping board, garnish with green onion. Enjoy!