In a mason jar or bowl, combine rolled oats and chia seeds.
In a separate bowl, mix the milk, cocoa powder, honey, vanilla extract, and salt until well combined.
Pour the chocolate mixture over the oats and chia seeds.
Stir well to ensure all oats are coated.
Cover the jar or bowl with a lid or plastic wrap.
Place in the refrigerator and let it sit overnight (or at least 4 hours).
In the morning, stir the oats to combine.
Add more milk if desired for a creamier texture.
Top with your choice of sliced banana, nuts, or berries.
Enjoy your delicious chocolate overnight oats cold!