Heat the oil in a saucepan, add the onion, red pepper and garlic and cook until soft. Stir in the rice, then add the stock and season to taste with salt and pepper.
Bring to the boil, then reduce the heat and simmer, stirring occasionally, for 10–15 minutes until all the stock has been absorbed and the rice is tender.
Stir in the sweetcorn and tuna and cook briefly over a low heat to heat through. Serve immediately garnished with the spring onions.