Preheat the oven to 180°C.
Combine the beaten egg, Greek yoghurt and milk in a mixing bowl and whisk together.
Add in the flour, sweetener and cinnamon, and whisk until you have a smooth batter.
Once the batter is smooth, add the sliced apples and mix until they’re coated.
Spray the oven or pie dish with some low-calorie cooking spray and pour in the apple batter mixture.
Pop in the oven for 30 minutes, until the top is lightly golden and the pie is firm and set.
Leave to cool for 5 minutes, then slice and serve with your choice of accompaniment. We love it with a scoop of low-calorie vanilla ice cream.