Place the rolled oats and chia seeds in a clean 16-ounce jar or medium bowl. Level the measuring spoons and cups so the mixture does not become too thick.
Add the milk and Greek yogurt. Dairy milk, oat milk, soy milk, or almond milk will work.
Add the maple syrup or honey, vanilla extract, and salt. Use 1 teaspoon of sweetener when serving the oats with sweet fruit. Use 2 teaspoons for a sweeter breakfast.
Stir for 30–45 seconds, scraping the bottom and sides of the container. Check that the chia seeds are evenly spread and no dry pockets remain.
Cover the jar or bowl tightly. Leave about 1 inch of empty space at the top because the oats and chia seeds will swell.
Place the container on a level refrigerator shelf for at least 6 hours, or leave it overnight for the softest texture.
Stir the oats before serving. Add milk 1 tablespoon at a time if they are thicker than you prefer. Wait 1 minute after each addition before adding more.
Add fruit, nut butter, nuts, coconut, cinnamon, or another topping. Add granola and other crunchy toppings right before eating so they stay crisp.
