Mix all dry rub ingredients in a small bowl. Slice Lions Mane lengthwise in half. Preheat oven to 410 F. Heat cast iron pan on medium-high heat, add oil and allow to get warm. Place mushrooms in the pan for 90 seconds before adding a heavy press to Lion’s Mane. Cook for 30 seconds before gently pressing down on the pan. Using tongs, flip Lion’s Mane and let brown for 5 minutes. Sprinkle dry rub over Lion's Mane, searing each side. When the Lion’s Mane is browned, place the cast iron pan in the oven for 12 minutes.