To prepare cake, pour 1/2 cup boiling water over tea bags in a bowl; steep 5 minutes. Remove and discard tea bags; cool tea to room temperature.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, baking soda, and salt, stirring with a whisk.
Place egg whites in a large bowl; beat with a mixer at high speed until foamy. Add granulated sugar and brown sugar; beat well. Add brewed tea, applesauce, and canola oil; beat until well blended. Gradually add flour mixture; beat just until moist. Fold in walnuts. Pour batter into an 8 x 4-inch loaf pan coated with cooking spray. Bake at 350° for 50 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 15 minutes on a wire rack; remove from pan. Cool completely on wire rack.
To prepare glaze, combine powdered sugar and rind in a small bowl. Add juice, stirring with a whisk until smooth. Drizzle glaze over cake; let stand until set.