Adjust oven shelf to lowest position; place an oven tray on the shelf. Preheat oven to 180°C/350°F.
Triple-sift flour into a medium bowl.
Process tea leaves and ¾ cup (165g) of the sugar until leaves are finely chopped. Transfer mixture to a small bowl of an electric mixer fitted with the whisk attachment, add egg yolks; beat for 5 minutes or until thick and pale. Gradually add juice, oil and half the rind, beating until well combined. Sift flour over mixture, then fold in with motor operating on low speed until just incorporated.
Beat egg whites in a large bowl with electric mixer until soft peaks form. Add cream of tartar, then gradually add remaining sugar, beating until mixture is thick and glossy. Fold egg white mixture into yolk mixture, in two batches, until just combined. Spoon mixture into an ungreased 25cm (10in) angel food cake pan with a removable base; smooth the surface.
Place cake pan on heated oven tray; bake cake for 50 minutes or until a skewer inserted into the centre comes out clean (cover with foil if necessary to prevent over-browning). Place a piece of baking paper, just larger than the pan on a work surface. Immediately turn hot pan upside-down on the paper; leave to cool completely in this position.
Meanwhile, make lemon icing.
Carefully run a small knife around the edge of cake and the tube to help release cake from pan (you may also need to run a knife or spatula between the base and the cake).
Place cake on a cake plate or stand. Spoon icing on top of cake, allowing it to drip down over the edge a little. Stand for 20 minutes or until icing is set. Decorate with flowers, if you like.
Sift icing sugar into a medium bowl. Gradually add juice, stirring until icing is the consistency of thickened cream.