In a mason jar or airtight container, combine the rolled oats, milk, Greek yogurt, and chia seeds (if using).
Add sweetener to taste, such as honey, maple syrup, or agave nectar. Stir well to combine all ingredients.
Customize your overnight oats with flavorings of your choice, such as a dash of cinnamon, a splash of vanilla extract, or cocoa powder for a chocolatey twist.
Add your favorite toppings, such as sliced fruits, nuts, seeds, nut butter, or shredded coconut, to add texture and flavor.
Seal the mason jar or container with a lid and refrigerate overnight, or for at least 4-6 hours, to allow the oats to soak and soften.
In the morning, give the overnight oats a good stir and enjoy them cold straight from the fridge, or you can heat them up in the microwave if desired.