Preheating the oven to 200°/180° fan, and line a 20cm baking dish with baking paper.
In a large bowl, mash 2 ripe bananas using a fork. Add the peanut butter to the bowl and mix well.
Add the seeds and oats to the bowl (you can do this all at once or a bit at a time), and continue to mix together well until all combined.
Press the mixture into your prepared baking dish. You can press some extra nuts or seeds into the top, or leave it as it is*.
Bake in the preheated oven for 18-20 minutes until golden. Cut into 12 squares whilst still warm, and leave to cool before eating.
*I like to top my breakfast bars with walnuts, pecans, pumpkin seeds or dark chocolate chips. My top tip when making these breakfast bars is to let the mixture sit in the baking dish for a little while before cooking. This allows the oats to soak up some of the moisture from the bananas, meaning the bars stick together even better after cooking.Bars will keep in the fridge for up to 5 days, and in the freezer for up to 3 months. Thaw before eating.