Juice the oranges until you have one cup of fresh juice (about 5 minutes).

In a mixing pitcher, combine the fresh orange juice and granulated sugar. Stir until the sugar dissolves completely, about 1–2 minutes.

Mix in the tablespoon of lemon juice to add extra zest.

Gently pour in the club soda or sparkling water, adding it slowly to preserve the carbonation.

Using a spoon, gently stir the mixture until everything is well combined, about 30 seconds.

Taste the soda and adjust the sweetness if necessary by adding more sugar and stirring until dissolved.

Fill glasses with ice and pour the orange soda over the ice.

Garnish each glass with a slice of orange or a sprig of mint, if desired, and serve immediately.