Add instant coffee, cocoa powder, sugar, and hot water into a bowl.
Whisk vigorously for 3–5 minutes until thick, glossy, and fluffy.
Drizzle chocolate syrup lightly into the whipped mixture.
Fold gently twice to create a visible swirl.
Fill two glasses with ice cubes.
Pour 150 ml cold oat milk into each glass.
Spoon mocha swirl whipped coffee on top.
Stir slowly before sipping, or admire the swirl like a masterpiece.