Combine Ingredients: In a jar or airtight container (like a mason jar), add the rolled oats, cocoa powder, chia seeds, sweetener, milk, vanilla extract (if using), and a pinch of salt.
Stir Well: Stir all ingredients thoroughly until everything is well combined and there are no dry clumps of cocoa powder or chia seeds at the bottom.
Chill: Cover the jar or container and refrigerate for at least 4 hours, but ideally overnight (8+ hours). This allows the oats to soften and the chia seeds to swell, creating a thick, pudding-like consistency.
Serve: The next morning, give the oats a good stir. If the consistency is too thick for your preference, add a splash more milk until it reaches your desired texture. Taste and adjust sweetness if needed.
Add Toppings (Optional): Enjoy your chocolate overnight oats as is, or personalize them with your favorite toppings. Some popular choices include fresh berries (raspberries, strawberries), sliced banana, a sprinkle of mini chocolate chips, chopped nuts, shredded coconut, or a dollop of yogurt.