Low-Calorie Cinnamon Drizzle Squares

You’ll need an electric hand whisk for best results and a rectangular baking tin (approx. 24 x 18 cm).
For the Cake
100 g self-raising flour (use gluten-free if needed)
50 g reduced fat spread (check for dairy-free if needed)
5 tbsp granulated sweetener (use a zero-calorie substitute that measures like sugar)
3 large eggs
2 tsp ground cinnamon
Low-calorie cooking spray
For the Cinnamon Drizzle
5 tsp icing sugar
½ tsp cinnamon
Water (added a few drops at a time)