Preheat the oven to 190°C, fan 170°C, gas mark 5. Brush the pepper halves with a little of the oil, place on a baking tray and bake for 10 minutes.
Meanwhile, add the remaining oil to a pan over a medium heat. Add the garlic and onion and fry for 5 minutes.
Add the rice and herbs, then stir in the tuna, sweetcorn and lemon juice.
When ready, fill the pepper halves with as much of the rice mixture as you can, patting it down.
Bake in the oven for 10 minutes, remove from the oven and top with the mozzarella.
Bake for 5 minutes more, or until the peppers are cooked and the cheese is melted. Serve with the bistro salad.