Preheat the oven to 180 degrees Celsius.
Cook the silverbeet in boiling salted water for 2 minutes. Plunge into cold water, squeeze dry, then blend in a food processor.
Stir through the nutmeg, fold in goat's cheese, then season with pepper and set aside.
In a glass or stainless steel bowl, beat the egg whites until they are stiff and form small peaks. Fold in the silver beet mixture, being careful not to overmix, then spread evenly across a baking sheet lined with baking paper.
Bake for 20-30 minutes until cooked through but still soft and springy to the touch.
While the spinach roll is cooking, heat the corn oil in a small pan and saute the mushrooms until they are soft. Add the tomato sauce and heat through. Ease the roll from the baking paper using a flat knife and spatula. Put it on a clean tea towel and lay the mushrooms and sauce over the top, leaving the edges clear. Carefully roll it up and serve warm with Italian green salad.