Fry the onion in the oil
until slightly brown. Add the water (should be boiled), pepper, salt
and let it simmer at low fire for about 5-10 minutes. Mix the
cornstarch with some water, and pour it into the soup. Stir for a
few minutes and the soup will thicken slightly. Toast the slices of
bread and put them on plates. Pour the soup on top and sprinkle with
the grated cheese.