1Using a zester, cut as many long strips of zest from the orange as you can and set them aside. Cut off and discard the remaining white pith, and cut the orange into 8 pieces.
2Place the orange pieces in a small bowl and sprinkle the sugar over them. Muddle until no large chunks remain. Divide the orange mixture among 4 iced tea glasses. Add 1/4 cup of Grand Marnier to each glass and stir well.
3Fill each glass halfway with ice. Divide the reserved zest among the glasses, then fill the rest of the way with ice. Fill the glasses with iced tea and serve with a lemon wedge.