Bring four cups water to a rapid boil in a teapot or saucepan. Remove from heat and add tea bags. Allow tea bags to steep for several minutes before discarding.
To prepare the infused simple syrup, combine a quarter cup water, sugar, lemongrass, and cinnamon sticks in a small saucepan and place over medium heat. Simmer, stirring occasionally, until mixture is heated through and starts to thicken, approximately 4-5 minutes.
Remove from heat and pour through a fine mesh strainer to separate the solids from the liquid. Discard solids and set the remaining simple syrup aside to cool.
Combine the brewed tea, lemon juice, and remaining cup of water in a large pitcher. Add infused simple syrup, to taste, and stir to combine.
To serve, fill four chilled glasses with ice before adding the sweetened iced tea mixture. Garnish with lemon slices and sprigs of fresh mint, if using, and serve immediately. Enjoy!