Preheat your oven to 180°C (350°F) and grease a standard cake pan or line it with parchment paper.
Peel the bananas and place them in a blender with the sugar, lemon juice, and lemon zest.
Blend the mixture until it looks mostly smooth, with just a few small banana bits left.
Add the eggs and sunflower oil to the blender, then blend again until everything comes together.
In a large bowl, whisk the flour and baking powder together so the powder spreads evenly.
Pour the banana mixture into the bowl with the dry ingredients and gently stir until smooth.
Scrape the batter into your prepared cake pan and spread it out evenly.
Bake for 35 to 40 minutes, or until a toothpick poked into the center comes out clean.
Let the cake cool in the pan for 10 minutes, then move it to a wire rack to cool completely.