Separate any clumps of mushrooms and tear any large pieces into smaller bite side bits. Heat the butter and oil in a large wok or frying pan. When hot add the mushrooms and cook for about 5 minutes until just done. Pour in the soy sauce and lemon juice, cook for a minute more then transfer to a serving plate.
Grind over a little fresh black pepper and scatter over the lemon zest and chives before serving.
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