Raw and cooked mushrooms can be frozen at home. The method is slightly different depending on if they are frozen before or after cooking them.
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.