Preheat oven to 220 C (430 F) and line a baking tray with baking paper.
Use a small cookie cutter to cut circles from the pastry sheets and place half of them on prepared baking tray.
Mash banana and avocado together until smooth.
Place small spoonfuls into the center of the pastry circles on the baking tray.
Gently place the other half of the circles on top.
Press the edges together with a fork.
Bake for about 12 minutes, or until puffed and golden.