Do you remember the buzz these two Berkeley kids created by selling a box of coffee grounds that will grow tasty mushrooms? When our box gave up its last oysters, I took the mycelium and inoculated our garden with it. This year, I'm being rewarded with some new oyster mushrooms!
Adding mushrooms to a raised bed garden is simple. do a little research and learn what sort of stuff your desired mushroom grows upon (oysters: oak, maple) and stuff some of the host material into the moist corners of your garden. Prep it well (make it good and wet, in most cases). Buy plugs, or look for living mycelia. Inoculate the host matter... and then wait. In a year or less you might have a new, renewable source of mushrooms!
BTW, did you notice how low effort this is?