Avena is the Spanish word for "oatmeal". In Nicaragua, Colombia, and some other Latin American countries, the word is used to refer to a drink prepared using oatmeal.
To prepare, water or milk is brought to a boil. Sugar and a small amount of oatmeal is added and cooked. If water is used, some amount of milk may optionally be added at the end of cooking. The oats may then be strained out, blended using a blender, or simply allowed to settle to the bottom of the pitcher. Cinnamon is sometimes used as well.