Preheat the oven to 180C/350F/Gas 4.
For the risotto cakes, put the ready-cooked rice into a bowl along with the remaining risotto ingredients, except for the oil, and stir well.
With wet hands, roll walnut-sized pieces of the risotto mixture into balls.
Heat the oil in a frying pan over a medium heat, and fry the risotto balls for 4-5 minutes, or until golden-brown on all sides.
For the roasted tomatoes, heat the oil in a separate, ovenproof frying pan over a medium heat and add the tomato halves, cut side down. Fry for 1-2 minutes, then transfer to the oven and roast for 7-8 minutes.
For the garnish, heat the olive oil in a frying pan over a medium heat and fry the sage leaves for 1-2 minutes, or until crisp.
To serve, place the risotto cakes onto a serving plate with the roasted tomato halves. Sprinkle the fried sage leaves over the top to garnish.