In a food processor or a blender, mix tomatoes, cucumbers, yellow pepper, and radishes.
Season with lime juice, ginger, fish sauce, palm sugar, and herbs. Mix well together to make a smooth puree. Slowly and gradually add coconut milk to the mixture.
Taste and adjust your recipe to your liking. For more sweetness, add coconut milk or for a spicier soup, add more chili.
Pour into a large bowl and refrigerate for a few hours. Let the flavors infuse and the soup becomes very cold to touch.
Garnish with tuna, additional herbs or pepper flakes and salt and pepper to taste.