Steep the tea bag in the boiling water for 2 to 3 minutes. Strain and let cool.
In a medium bowl, mix the cream cheese, walnuts, 1/4 cup mint and 4 to 5 tablespoons brewed tea into a paste. Season to taste with salt.
Lightly butter each bread slice on 1 side and cut each slice into 4 squares. Place a cucumber slice on the buttered side of the bread, top with the cream cheese mixture and garnish with a mint leaf.