Oh I see you ID'd them. I was going to suggest that. We get mushrooms when we buy miracle grow potting soil for the houseplants (we now avoid that like the plague) I can see how a spore or two can get in then infest the whole area. We get little grown mushrooms all over due to rains, but nothing poisonous! How poisonous are they? Meaning if it's resting on a lettuce leaf can it make you sick when you eat the lettuce?
I'll see if I can find any info on this.
---------- Post added at 02:27 PM ---------- Previous post was at 01:52 PM ----------
OK I found this...
What Is This Thing in My Yard (Garden, House)? [MushroomExpert.Com]
he says no mushroom is so poisonous it'll hurt you just from touching it. So as long as you wash your hand and veggies it should be fine.
BUT he also says there is no way to get rid of them. So I'm not sure what to suggest. To get rid of our indoor mushrooms we dumped all the potting soil out, washed the pot and the roots of the plants and then re-potted and the problem went away. Normally mushrooms are a good sign, meaning your soil is healthy and nice. But poisonous mushrooms, I'd worry too. you can try a fungicide, but I'm not sure how well that will work. I would wait until the season is oven then use a fungicide and then use it again as soon as the bottle says too. See if that works. Plus leave the garden bed open over winter (or summer, whatever you have since you're not in the northern hem.) Don't cover it with anything, like winter crops or mulch. It will not be good for the garden but the sun hitting it and keeping it dry may help keep the fungus down.