Prep lion's mane mushrooms by removing any tough bits of substrate on the bottom and slicing or ripping into thick slices/pieces, at least 2-3 inches thick.
Heat a cast iron skillet over medium heat and add 1 tablespoon of vegan butter or oil, just enough to lightly coat the bottom of the pan.
Add mushrooms to pan in a single layer, let cook for about 2 minutes untouched and then add another heavy pan, weight or panini press on top of the mushrooms and cook another 3-5 minutes. (see note about mushrooms with excess moisture).
Carefully remove weight (make sure not to burn yourself and carefully wipe away any condensation). Flip mushrooms and add ½-1 tablespoon of butter or oil all around them (but not on them) and re-apply weight. Cook another 4-5 minutes.
Once both sides have a nice, golden brown crisp, add 1 tablespoon of tamari and stir to coat, cooking 1-2 minutes longer until any remaining liquid is evaporated. Top with a light sprinkle of sea salt to taste and serve!