In a jar or container with a lid, combine rolled oats, unsweetened almond milk (or your preferred milk alternative), ground cardamom, ground cinnamon, chia seeds, nut butter, maple syrup, and salt.
Stir the ingredients until well combined, ensuring that the oats are fully submerged in the liquid.
Seal the jar or container with a lid and refrigerate overnight, or for at least 6 hours, to allow the oats to soften and absorb the flavors.
In the morning, give the oats a good stir. If desired, you can add more almond milk to achieve your preferred consistency.
Serve the overnight oats cold straight from the fridge, or warm them up in the microwave or on the stovetop if you prefer them warm.
Optional: Garnish with your favorite toppings such as fresh berries and/or sliced bananas.