Prepare the blueberries by rinsing them thoroughly under cold water and removing any stems or damaged berries. Pat them dry with a paper towel.
Place blueberries in a cocktail shaker or mason jar and gently muddle them using a muddler or the back of a wooden spoon. Press just enough to release their juices without completely crushing them to a pulp.
Add the fresh lemon juice, honey/simple syrup, and lemon zest to the muddled blueberries. Stir or shake gently until the honey is completely dissolved.
Strain the mixture through a fine-mesh strainer into a pitcher or directly into ice-filled glasses, pressing gently on the solids to extract all the juice. This creates a smoother drink without pulp, but you can skip straining if you prefer more texture.
Fill two tall glasses halfway with ice, then pour the blueberry-lemon mixture evenly between them, filling each glass about one-third full.
Top each glass with chilled sparkling water, pouring slowly to maintain the fizz. Gently stir once to combine the flavors without losing carbonation.
Garnish with fresh blueberries, a lemon slice, and mint leaves if desired. Serve immediately while the drink is still bubbly and cold.