Saute the mushrooms with onions, garlic and parsley in olive oil, season well and whiz into a rough paste. Take the fillet and hold flat with the palm of your hand on to a chopping board. Take a sharp knife and cut a slit side lengthwise. Continue slicing and turning the pork fillet until you have obtained an even flat surface. Season the pork with salt, pepper and lemon zest. Spread with the ricotta cheese and the mushrooms. Roll the fillet tight and wrap around with the Parma ham. Roll tightly in cling film and poach for 15 minutes. Remove from cling film and toss in a pan with a knob of butter, finish cooking in a hot oven until ham is crispy and pork is done. Cook the shallot in a few drops of olive oil until soft, add the parsnips and apple with the sugar, caramelize for a few seconds. Cover with water and cook until soft. Remove excess water and whizz into a creamy puree.