If the mushrooms are raw, clean them first. Chop them into slices that are less than ½-inch thick. Spread them on a plate in a single layer, trying to avoid overlapping. Freeze them for two hours in this state, then transfer them to a freezer container. This helps them stay loose instead of turning into one big clump.
To freeze cooked mushrooms, cut them into pieces, and cook on a skillet over medium-low heat until the mushrooms release their liquid. Let them cool to room temperature, then transfer to freezer containers.Learn more about Freezing Food