Bring 6 cups of water to a boil in a tall pot.

Add 1 cup of rolled oats to the boiling water.

Cook the oats, stirring occasionally, until a thin oatmeal forms, about 5 minutes.

Remove the pot from heat.

Stir in 2 cups of cold water, 1 (14 ounce) can of sweetened condensed milk, and 2 tablespoons of vanilla extract.

Transfer the oat mixture to a pitcher.

Chill in the refrigerator until cold, at least 1 hour.

Pour the drink into glasses.

Sprinkle ground cinnamon over the top before serving.