Wash the orange thoroughly, then zest it with a microplane, taking only the bright orange outer layer and avoiding the bitter white pith. Set aside 1 tablespoon of zest, cut the orange in half, and squeeze 2 tablespoons of fresh juice into a separate container, removing any seeds.
In a mixing bowl or mason jar, combine the milk, Greek yogurt, fresh orange juice, honey or maple syrup, and vanilla extract. Stir with a spoon or whisk until the yogurt is fully incorporated and the mixture is smooth.
Add the rolled oats, orange zest, chia seeds (if using), ground cinnamon, and a pinch of salt. Stir thoroughly until all the oats are coated and no dry oats remain at the bottom.
Gently fold in the dried cranberries, distributing them evenly and making sure they are submerged in the liquid. Reserve a few cranberries for topping if desired.
Divide the mixture evenly between two mason jars or airtight containers if you mixed in a bowl. Press down gently so all oats are covered by liquid, adding a splash more milk if any oats stick up above the liquid line, then seal tightly.
Place the sealed jars in the refrigerator and let them sit for at least 6 hours, ideally 8 hours or overnight, so the oats soften, the cranberries plump up, and the orange flavor infuses throughout.
Remove from the refrigerator, stir well to redistribute any settled liquid, and taste to adjust sweetness with more honey or maple syrup if needed. Top with sliced almonds, fresh cranberries, and extra orange zest, then enjoy cold or warm in the microwave for 45-60 seconds.