Fill a large cocktail shaker halfway full of ice.
Set aside two halves of the passion fruit for garnish. Scoop out the remaining seeds and pulp and add them to the cocktail shaker, reserving two teaspoons of pulp in a separate small bowl.
Combine the orange, grapefruit, lime, agave syrup, N/A spirit in the cocktail shaker. Slap two mint sprigs to express the oils.
Shake, shake shake for 10 to 15 seconds or until the shaker tin is nice and cold.
Fill highball glasses with ice.
Add your drink so it fills the glass halfway. Stir in the reserved passion fruit seeds and pulp with a cocktail stirrer or long-handled spoon. Top with seltzer.
Scoot the lime wheels flat up against the sides of the highball glasses to make them visible.
Garnish each glass with a half passionfruit, cut side up, and a sprig of mint.