In a 16-ounce glass jar, combine the rolled oats, chia seeds, poppy seeds, and salt.
Add the almond milk, Greek yogurt, lemon juice, lemon zest, maple syrup, and vanilla extract to the dry ingredients.
Stir vigorously with a spoon or seal the jar and shake until the mixture is uniform.
Secure the lid tightly and place the jar in the refrigerator.
Allow the mixture to hydrate for a minimum of 6 hours, preferably overnight.
Remove from refrigeration, stir to redistribute moisture, and adjust consistency with additional milk if desired.