Prepare Tomatoes: Fill a large bowl with ice water. Bring a pot of water to a boil. Cut a small "X" at the bottom of each tomato and immerse them in the boiling water for 30 seconds. Using a slotted spoon, transfer the tomatoes to the ice water for 1 to 2 minutes. The skins should peel off easily. Remove and discard the skins, then chop the tomatoes into pieces.
Combine Ingredients: In a large bowl, mix the tomatoes, cucumber, red bell pepper, shallot, garlic, olive oil, lemon juice, sea salt, and black pepper. Stir well and let the mixture sit for at least 20 minutes to enhance the flavors. Stir occasionally.
Blend and Chill: Pour the mixture into a blender and blend on high until smooth. Refrigerate for at least 2 hours.
Serve and Garnish: Pour into bowls and garnish with chopped fresh basil.