Put the rooibos tea with the peppermint leaves and the ginger in a bowl and add the boiling water. Let the tea steep for 5 minutes, then drain through a sieve and refrigerate for three quarters of an hour.
Wash the lemons with hot water, rub dry and cut each in half. Slice 1 lemon and squeeze the other. Mix the tea with the lemon juice and sugar.
Pour the tea into a glass with ice cubes and lemon wedges and serve with fresh mint.