Preheat the oven to 180°C.
Chop the soaked mushrooms and mash them to a paste using a pestle and mortar.
Blitz the mushroom paste, vinegar, onion, garlic, herbs, sugar, salt, and pepper in a blender.
Lay bacon rashers side by side to form two sheets and place a lamb fillet on each center.
Spread the paste over the lamb and roll each fillet tightly inside the bacon sheets.
Place fillets in a roasting tin and roast for 15 to 25 minutes depending on preference.
Remove lamb from the oven and rest in a warm place for 10 minutes.
Slice the lamb on a diagonal and serve with mashed potatoes and roasted vegetables.