Combine dry ingredients: In a medium mixing bowl or directly in a mason jar, add the rolled oats, chia seeds (if using), cinnamon, and a small pinch of salt. Stir these together to evenly distribute the spices and seeds so they don’t clump later.

Add wet ingredients: Pour in the milk, Greek yogurt, and vanilla extract. Stir slowly but thoroughly until all the oats are coated with liquid and there are no dry spots. This step ensures the oats soften evenly overnight.

Sweeten it up: Add the brown sugar and whisk or stir until it completely dissolves into the mixture. If you want a stronger caramel-like flavor, use dark brown sugar; for a lighter sweetness, stick with light brown sugar.

Transfer to containers: Divide the mixture into two jars, glasses, or airtight containers. Make sure the oats are fully submerged in liquid—if not, add a splash more milk. Smooth the tops with a spoon so they set nicely.

Chill overnight: Cover the jars tightly with lids or plastic wrap and place them in the refrigerator for at least 6 hours, preferably overnight. This allows the oats to slowly absorb the liquid, soften, and take on the sweet brown sugar flavor.

Serve and top: In the morning, give the oats a gentle stir. You can enjoy them cold straight from the fridge, or warm them up in the microwave for about 30–60 seconds if you prefer. Add your favorite toppings—banana slices, walnuts, raisins, or even an extra sprinkle of brown sugar for a crunchy finish.