Pre-heat oven to 190 C, 375 F, Gas mark 5. Drain the can of salmon and flake the fish into a bowl. Mix in the tomatoes and the finely chopped chillies. Arrange the nachos onto a baking tray and pile equal amounts of the salmon and chilli mixture over them. Top this with half a teaspoon of natural yogurt or sour cream and sprinkle with the cheese. Bake in the oven for 6-7 minutes or until the cheese is just bubbly. Serve hot. Serves 10-12. Approx. 180 kcals per serving