01 - In a medium bowl or jar, combine the oats, milk, Greek yogurt, brown sugar, cinnamon, and vanilla extract. Stir thoroughly until all ingredients are well incorporated and the brown sugar has dissolved.
02 - Cover the bowl or jar securely with its lid. Refrigerate for at least 8 hours, preferably overnight, to allow the oats to soften and absorb the liquid.
03 - Remove from refrigeration. Stir the oats thoroughly and assess the texture. Add a small splash of milk if the mixture appears too thick, stirring again to reach your desired consistency.
04 - Top with banana slices, chopped walnuts or pecans, and fresh berries or apple slices if desired. Serve immediately while chilled.