Place your Tomatoes, Onion, and 1/2 of your Pepper, on a baking sheet and broil for about 8 minutes turning halfway through to get them charred on all sides. Remove and set the onion and tomatoes aside to cool and place the 1/2 pepper in a plastic bag to steam. When cool enough to handle core the tomatoes and add to the blender with the onion. Peel the pepper and add it to the blender as well. Peel the cucumber and cut lengthwise, remove the seeds and add 1/2 of the cucumber to the blender. Chop the other half of the cucumber and the other half of the pepper and set aside. Add the rest of the ingredients to the blender and blend until smooth. Pour into a large pitcher or bowl and add the chopped cucumber and pepper to the mixture. Refrigerate for a couple of hours. Serve cold with a green onion garnish.