Wipe clean the mushrooms and trim off the end of the stem. Cut into slices, halved if large. Finely chop the onion and crush or finely chop the garlic.
Fill a wide pot with boiling water and add the gnocchi, part at a time if making more than one serving. Increase the heat, if needed, to bring water back to a simmer. Once the gnocchi float to the top, remove from the water, draining as you do so, and set aside in a bowl.
Meanwhile, warm half of the butter in a small-medium skillet/frying pan. Add the onion and cook a couple minutes, stirring regularly, until onion is softened.
Add the rest of the butter and part of the mushrooms. Stir to soften the mushrooms then add the rest once there is a bit more space (they reduce in size as they cook). Add the garlic, oregano and a little salt and pepper.
Cook for a couple minutes until the mushrooms have released their liquid, this evaporates off and the mushrooms start to brown slightly. Add in the cooked gnocchi, stir then add the stock. Simmer for a minute or two to reduce slightly then add the parsley, stir through and serve. Optionally, add some cheese on top.
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Notes
You can easily make larger quantities of this to serve more people - just multiply everything up and use a larger skillet to cook the mushrooms etc. Cook the gnocchi in batches so as not to overcrowd the pot and reduce the temperature too much.