Heat a large skillet over medium-high heat. Add the mushrooms to the dry, hot pan in a single layer. Stirring occasionally, allow the mushrooms to cook until they release all of their liquid and the liquid has evaporated from the pan. About 5 minutes.
Once there is no liquid left in the pan add the butter, olive oil, Tamari or soy sauce, and garlic to the cooked mushrooms. Continue to saute for about 2 minutes until the mushrooms are golden brown and there is no liquid left in the pan.
Turn off the heat, season with salt and pepper if desired then toss with parsley.