Clean any dirt off the mushrooms and give a quick rinse, shake off any water. Slice closed mushroom in half lengthwise, and for open mushrooms, cut in half at the stem, then slice the two piece in half lengthwise through the stem. Place in a large mixing bowl.
Add a good shake or two of black pepper then pour in about 1/2 cup teriyaki sauce (and I cannot stress enough to make your own as well). Give the mushrooms a mix with your hands, then let sit on the counter for 20-30 minutes.
Heat a non stick pan, no oil is needed. When the pan is hot, add the mushrooms, just pour the mushrooms and sauce that was not absorbed into the pan.
Stir fry for a few minutes to get them all heated through and they will release their water and the teriyaki sauce.
Simmer on medium to medium low heat, stir often, the open mushrooms release a lot, and I mean a lot, of water.
When most of the water is cooked off, add the remaining 1/2 cup of teriyaki sauce and stir that in.
Continue simmering to reduce the liquid a bit more.
Use a slotted spoon and spoon out the mushrooms to a serving dish or add as a side to plate, enjoy.