Preheat the oven or air fryer to 180°C. Line one medium loaf tin or two small loaf tins with baking parchment.
Mash the bananas thoroughly in a large mixing bowl.
Add the eggs, vanilla extract, lemon zest and lemon juice, then mix until well combined.
Stir in the wholemeal flour, oats and poppy seeds until evenly mixed.
Leave the batter to rest for 5 minutes so the oats can absorb some of the moisture.
If the mixture seems too thick, add a splash of milk or plant-based milk. If it is too loose, stir in a little extra oats.
Spoon the batter into the prepared tin or tins and level the surface.
Bake for about 25 minutes if using two small loaf tins, or 45 minutes if using one medium loaf tin, until lightly golden and a skewer inserted into the centre comes out clean.
Air Fryer Method:Bake in a silicone or air fryer-safe loaf tin at 180°C for about 25 minutes (for a small loaf), or until the cake is golden and cooked through. Check with a skewer before removing from the air fryer.
Leave the cake to cool in the tin for 10 minutes before transferring it to a wire rack to cool completely.
Slice and serve.