Steep the green tea leaves or the bags in 1 cup of hot water for 2-3 minutes. Add sugar to the hot tea and stir well until dissolved.
Pour the green tea mixture into a large glass bottle. Let it cool in the fridge.
Once the green tea mixture is completely chilled, take it out. Squeeze some juice out of the lemon. Pour the lemon juice into the bottle. Add sparkling water. The green tea lemonade is done!
Fill glasses with ice cubes and pour the green tea lemonade over. Garnish it with lemon slices and mint leaves if desired.