Halve the sausages lengthways. Cut in the ends so that they fan out when roasting and cut into the sausage skin crosswise. Peel the onion and cut into rings.
Fry the sausages on both sides in a pan. Then place the halves of the sausage on 4 plates, distribute the onions on the sausages and top with ketchup or salsa if you like. Place the cheese on the sausages and sprinkle with curry if you like. Microwave for 1 minute at 600 W.