In a medium bowl, combine the rolled oats and chia seeds. Whisk them together to ensure the chia seeds are evenly distributed.

Pour in the almond milk and add the almond butter and maple syrup. Stir everything together thoroughly until the almond butter is well incorporated and no lumps remain.

Gently fold in the mixed berries. If using frozen berries, they will thaw overnight and release some juice, adding more flavor and color to the oats.

Divide the mixture evenly between two jars or airtight containers.

Cover the jars tightly and refrigerate for at least 4 hours, or preferably overnight, to allow the oats and chia seeds to absorb the liquid and thicken.

Before serving, stir the overnight oats. If they are too thick for your liking, you can add a splash more almond milk (about 30ml or 2 tbsp) to reach your desired consistency.

Top each serving with sliced almonds and an extra handful of berries, if desired, for added texture and freshness.