Pre-heat the oven to Gas Mark 4, 180°C, 350°F.
Heat 1 tbsp oil in a frying pan. Add the minced lamb. Break up the mixture with a wooden spoon to stop large clumps forming.
Brush the mushrooms. Remove the stalks and chop them. Add the stalks into the frying pan.
Take the pan off the heat when everything is browned and transfer to a dish. Add the ricotta and pesto. Mix and season to taste.
Lightly oil the mushrooms and stuff them with the mince mixture. Place them in an oven dish and cook for 10 minutes.
Sprinkle over the grated cheese then the chopped pine nuts and continue to cook in the oven for around 10 minutes.
Serve hot as a starter or snack, accompanied by a salad.