Preheat the oven to 180°C/fan160°C/gas 4. Drain half the oil from tuna into a flameproof casserole. Discard the rest of the oil. Add onion and bacon. Cook over a medium heat for 8 minutes, stirring, until the onion is turning golden.
Stir in rice, cook for 1 minute, then stir in pasta sauce. Add the drained tuna, pour over 500ml boiling water from the kettle and season with black pepper. Stir gently, cover and bake for 30 minutes, until the rice is tender. Scatter with some finely sliced basil leaves to serve, if you like.