Heat the oil in a large heavy based casserole pan over a medium, high heat. Season the chicken legs and place in the pan, brown on all sides until they are a golden colour. This will take about 8 minutes. Remove and set aside on a plate.
Reduce the heat slightly and add the butter. When it begins to foam, add the bacon and fry until just crisp. Add the garlic and onion and fry for 3–4 minutes. Add the mushrooms and cook for a further 3 minutes.