Cook the rice and keep hot. Heat the
butter in a saucepan and fry the onions till soft, without browning.
Leave half of the onions in the saucepan and add the other half to the
rice, together with the beaten egg, salt and pepper and cook for
several minutes until the egg is just set. Press the rice into a ring
mould and turn out on to a serving plate. Add the tuna, with the green
peas and tomato ketchup to the remainder of the onion in the saucepan
and fry for a few minutes till well mixed. Dish on to the centre of
the ring. Garnish and serve.