In a nonreactive bowl, combine tomatoes and their juice, cucumber, garlic, bell pepper, beet, red onion, lemon juice, sherry vinegar, salt and pepper.
Use your hands or a potato masher to crush the ingredients slightly.
Cover the bowl and refrigerate overnight.
Transfer the mixture to a blender in batches, and purée. While blending the last batch, slowly pour in the olive oil. Strain the soup through a fine—mesh sieve into a clean bowl. Taste the soup and add salt, pepper and /or vinegar, as needed.
Ladle in to bowls and garnish with avocado and a drizzle of olive oil.