Fill a tall glass with fresh ice and set it aside. This keeps the drink cold without watering it down.
Add about 1 cup of ice to a lidded jar or cocktail shaker. Add 100 ml of concentrate, 1 tbsp of syrup and ⅛ tsp of cinnamon.
Seal the lid tightly and shake until the jar feels frosty and the coffee looks lighter, with a thin foam on top.
Pour the coffee into your glass and leave the used ice behind.
Pour in 120 ml of cold oat milk and let it cascade through the coffee. Stir, or leave the layers.
Add a few drops of syrup for more sweetness, or a splash of concentrate for a bolder cup.