Preheat the oven to 200C/180C fan/Gas 6. Place the halved red peppers skin-side up on a baking tray with the quartered onion and whole garlic cloves. Drizzle with 1 tablespoon of olive oil.
Roast for 25 minutes until the pepper skins are charred and blistered. Remove from the oven and leave until cool enough to handle, then peel off the pepper skins and discard them.
Put the roasted peppers, onion and garlic into a large saucepan. Add the chopped tomatoes, stock, oregano and the remaining olive oil.
Bring to a simmer and cook for 10 minutes. Blend until smooth with a stick blender or regular blender.
Season well with salt and pepper. Serve in warm bowls with crusty bread.