Combine first 3 ingredients in a medium bowl; stir well.
Cover and steep 5 minutes.
Strain tea mixture through a fine sieve into a bowl; discard tea leaves.
Stir lemon juice into tea; cover and chill.
Pour tea into the freezer can of an ice-cream freezer, and freeze according to manufacturer's instructions.
Spoon sorbet into a freezer-safe container; cover and freeze sorbet at least 3 hours or overnight.