Crumble bread and place in blender or food processor. Add vinegar and blend. Add garlic and sugar, then blend again. With blender or processor running slowly, add as much olive oil as bread will absorb without becoming oily. Add tomatoes, tomato juice, spring onions, cucumber, red pepper, and chopped basil; blend. Pass through strainer and dilute with ice cubes. Season with salt and white pepper. Avocado and Basil Sorbet: Puree avocados with lemon juice. Dissolve sugar in water. Add salt, pesto, and basil. Blend ingredients in food processor until smooth. Put in ice cream machine or in tub in freezer. If in tub, remove from freezer to stir when mixture starts to freeze, then return to freezer. Pour bisque into 4 cold soup bowls, adding scoop of avocado and basil sorbet to each. Decorate with basil leaves.