In a blender container, combine the avocado, half of the cucumber, the white part of the scallion, half the jalapeno, water and salt.
Blend until smooth.
With the motor running add lime juice, tequila (if using), cilantro and mint; blend until smooth but still speckled with herbs; add additional water as necessary to get soup consistency.
Chill soup for at least 2 hours before serving.
Before serving, cut remaining cucumber half into 1/4-inch dice, slice green part of scallion.
Spoon the soup into bowls or small cups.
Top with dollops of sour cream and the diced cucumber and green onion.