Preheat your oven to 180°C (350°F) or 160°C (fan). Grease and line a rectangular tray bake tin (approx. 20x30 cm or 8x12 inches).
In a large bowl, mash the bananas until smooth. Set aside.
In a separate bowl, beat the butter and sugar together until light and fluffy. You can use an electric mixer or do it by hand.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In another bowl, sift together the self-raising flour, baking powder, cinnamon (if using), and salt.
Gradually fold the dry ingredients into the wet mixture until just combined. Be careful not to overmix. Gently stir in any optional add-ins like chocolate chips or nuts.
Pour the batter into the prepared tin, smoothing the top with a spatula. Bake for 25–30 minutes or until a skewer inserted into the centre comes out clean.
Allow the tray bake to cool in the tin for 10 minutes, then transfer it to a wire rack to cool completely.
If glazing, mix the icing sugar with milk or lemon juice to a pourable consistency and drizzle over the cooled cake.