In a jar or airtight container, combine the cashew milk, vanilla protein powder, chia seeds, cinnamon, and optional sweetener.
Stir thoroughly until smooth.
Let the mixture rest for 15 minutes, then stir again to break up any clumps.
Refrigerate overnight, or at least 6 hours, until thickened.
When ready to serve, stir the Greek yogurt with half of the liquid sweetener.
Spoon the yogurt into a serving bowl and top with the Apple Cinnamon Protein Chia Pudding.
In a small bowl, combine the diced apples, remaining sweetener, cinnamon, and lemon juice.
Spoon the apple mixture over the pudding.
Sprinkle with chopped walnuts and serve immediately.