Preheat your oven to 350°F (175°C).
In a large bowl, mash the bananas until smooth.
Add the soy milk, peanut butter, honey, vanilla, flax seeds, chia seeds, hazelnuts, and stevia. Mix well.
Stir in the oats until fully combined.
Spread the mixture into a lined baking dish and smooth the top.
Bake for 15–20 minutes, or until set.
Remove from the oven, let cool, and cut into squares.
For chewy oat bars, stop here.
For crunchy oat bars, transfer the cut squares into an air fryer and dehydrate for 4 hours.
Cool completely and store in an airtight container.