Wash and dry the spinach, discard the stalks and put the leaves into a shallow salad bowl. Put the canned anchovies and their oil into a large saucepan. Add the olive oil, warm very gently and crush the anchovies with a wooden spoon so they dissolve and disintegrate. Lightly toast the French bread on one side only. Paint the untoasted side with a little of the anchovy oil, then grill until gilded. Add 2 teaspoons lemon juice and a good grinding of pepper to the anchovy mixture remaining in the pan. Slice the mushrooms thickly and add them to the salad bowl. Pour on the anchovy dressing while still warm (use a plastic-bladed spatula to get every last drop formt he pan) and toss gently. Slice the mozzarella and add it to the salad just before serving. Garnish with the toasts or hand round separately, and offer wedges of lemon as well.