On a flat surface start an assembly line of 4 wrappers, the mushroom filling, and a small bowl of water handy.
Place 1 tablespoon of mushroom filling in the center of the wrapper. Using your finger brush the edges with water.
Lift 2 opposite corners of the wrapper and pinch them together at the top. Lift the other two corners towards the top and pinch them against the first two corners to form a pyramid. Pinch edges of the wrapper together to seal the wonton closed.
Transfer the sealed wontons onto a sheet pan and cover loosely with plastic wrap to keep them from drying out.
Repeat this method until all the wrappers have been filled.
To cook the wontons heat a few tablespoons of oil in a large skillet set over medium heat. I like to use a nonstick skillet.
When the oil shimmers, add the wontons and cook until the bottoms are light golden brown and crunchy (about 2-3 minutes).
Carefully pour 1/4 cup of water into the skillet and stand back in case of splatter. Immediately cover with a tight-fitting lid.
Turn heat to medium-low and let the wontons steam for 5-6 minutes.
Repeat this step for remaining wontons. Serve warm with dipping sauce and green onions (optional).