Carefully wipe ceps with damp kitchen paper. Finely slice, then lay them flat on a large plate. Mix lemon juice with water and seasoning, then whisk in extra virgin olive oil. Brush about half of this dressing over mushrooms with a pastry brush. Sprinkle with sea salt and grind over a little black pepper. Marinate for about 10 mins. Toss wild rocket and Parmesan shavings with the remaining dressing, season. Divide between four plates, then gently place ceps over the top.