Place the tomatoes, garlic, scallions, bread, vinegar and 1 cup (250ml) of water into a blender or food processor, and puree until smooth and silky. With the motor running, slowly drizzle in the olive oil and blend until incorporated. Add the salt and give it a quick blitz to combine. Check the texture is loose and pourable. If it is too thick, blend in a touch more water.
For cold: transfer the soup to a container, cover and chill until it’s cold, about 30 minutes. The soup can also be prepared ahead of time and stored in the fridge for several days. You can also serve immediately by adding ice cubes.
For hot: pour the soup into a large pot and gently heat on medium heat until it is warmed through. You can also heat up individual bowls in the microwave.
To serve, divide the soup among four serving bowls and top with scallions, a little olive oil and, if using, a drizzle of tahini and croutons or panelle.