Preheat the oven to 185'. Line a baking tray with baking paper.
Finley dice onion and saute until tender – allow to cool.
In a food processor, finely pulse remaining ingredients until combined, add onion and pulse till roughly smooth.
Cut pastry in half lengthwise, spoon filling into the middle and smooth down to be an even shape. Fold over pastry sides to cover the filling.
Place fold side down on a baking tray, then brush with oat milk and sprinkle with sesame seeds.
Bake for 30 minutes or until the pastry is golden.
