In a large mixing bowl, whisk together the Greek yogurt, whole milk, honey, vanilla extract, and salt until smooth with no streaks of honey left.
Add the chia seeds and whisk hard for a full minute so they spread through the mixture instead of clumping into one wet mass.
Cover the bowl and refrigerate for 30 minutes, then take it out and stir again to catch any seeds that sank to the bottom.
Cover again and refrigerate for at least 4 hours, or overnight, until the pudding is thick enough that a spoon stands up in it.
Once set, divide the pudding evenly among 4 jars or bowls, about 1 cup each.
Top each serving with 1/2 cup diced mango and a sprinkle of toasted coconut or chopped pistachios, if using.
Serve cold, straight from the fridge.