Preheat oven to 200˚C/400˚F/Gas Mark 6. If cooking an oven full of potatoes, increase the temperature to 220°C/425°F/Gas Mark 7.
Rub a little salt into the potato skins before baking, to make them extra crispy, then place in a pre-heated oven for 1 hour or until cooked in the middle.
When the potatoes are ready, heat the oil and gently fry the mushrooms for 3-4 minutes then set aside.
Either place the bacon under a pre-heated grill and cook for 2-3 minutes on each side or dry fry for 4-5 minutes. Cool slightly and roughly chop.
Halve the potatoes lengthways and scoop out the flesh. Mash the potato and combine with half the grated cheese and bacon and season to taste.
Place the mushrooms in the potato shells, pile on the potato mixture, sprinkle with the remaining cheese and return to the oven for 10-15 minutes until the top is lightly browned and the cheese is melted.