Preheat oven to 200°C/400°F/Gas Mark 5 and heat a ceramic roasting dish (or roasting pan lined with baking paper). Peel tomatoes by bringing a saucepan of water to the boil. Score a cross in tomato skins without cutting too deep into the flesh. Place tomatoes in boiling water, not overcrowding the pan, and count to 20. Remove tomatoes and place in a bowl of cold water. Leave for a minute, then peel skin off with your fingers; it should come away easily but if it doesn’t, return to the pan for 10 seconds. Cut tomatoes into quarters.
Put a few teaspoons of olive oil into the preheated roasting dish. Cut capsicums in half, remove seeds, and lay them cut-side up in the dish. Divide basil, garlic and spring onions between capsicums, then place three tomato quarters into each one, packing them in tight. Drizzle remaining oil over stuffed peppers and sprinkle with salt and pepper.
Bake 25 minutes until tomatoes have softened and capsicums have taken on some colour. Remove from the oven and leave to cool and mature for a few hours before eating, or store in the fridge for the following day when they’ll taste just as good.