Brew the tea base. In a medium saucepan, bring 4 cups of water to a boil. Remove from heat, add tea bags, cover, and steep for 5 minutes. The color should be a rich amber, but be careful not to over-steep or it may become bitter.
Remove tea bags and sweeten. Discard the tea bags and stir in your sweetener of choice while the tea is still warm. This ensures it dissolves completely. Allow the sweetened tea to cool to room temperature.
Prepare the mango purée. While the tea cools, add the diced mango to a blender or food processor and blend until completely smooth. For an extra-smooth texture, you can strain the purée through a fine mesh sieve to remove any fibrous bits.
Combine the elements. Pour the cooled tea into a large pitcher, add the mango purée and lemon juice, then stir thoroughly until well combined. Taste and adjust sweetness if needed.
Chill thoroughly. Refrigerate the Mango Iced Tea for at least 2 hours, or ideally 4 hours, to allow the flavors to meld and develop. The patience pays off with a more harmonious flavor.
Serve with style. Fill glasses with ice cubes, pour in the chilled tea, and garnish with fresh mint leaves and lemon slices if desired. Stir gently before serving to redistribute any settled mango purée.