Preheat the oven to 180c/350f.
Mash the bananas in an oven proof dish (you can make this thinner for younger babies by using a larger dish, or slice into thin finger strips to hold, just reduce the cooking time if making larger - we used a 7”x5” dish which yields a slice 1-1.5” thick slice).
Add the nut butter and mix with the banana.
Add the oats and stir to combine.
You can leave out the milk if you would prefer a chewier slice, however for younger babies or toddlers who have a preference for softer foods add the milk at this stage and stir through.
Top with the chia jam, or stir through berries.
Bake for 30 (+/- a couple minutes, it will look golden on the sides or bottom and will be firm to push) minutes and allow to cool before cutting into ~12 slcies and serving.
Store in an airtight container in the fridge for 5 days, bench for 2 days, or freeze individual portions for 3 months.
If it seems too soft to cut, leave to cool for 15-20 minutes as it firms up with time.