In a medium bowl, combine 1 cup of rolled oats and 2 tablespoons of cocoa powder. Add chia seeds if using. Stir until evenly blended.

In another bowl, mix together 1 cup of brewed coffee, 1 cup of milk, and 2 tablespoons of sweetener. Add Greek yogurt if desired. Whisk until smooth.

Pour the coffee mixture into the dry ingredients and stir well until all oats are coated and there are no dry patches.

Divide the mixture evenly into two jars or containers. Seal tightly with lids.

Place the jars in the refrigerator and let them chill for at least 4 hours or overnight.

In the morning, stir the overnight oats and add toppings like fruits, nuts, or cocoa powder before serving.