Make the filling by tipping the canned tomatoes and garlic in a small-medium saucepan. Simmer together for 10 minutes, stirring occasionally, then allow to cool. Stir through the cinnamon, chilli and tuna.
Unroll each pastry sheet, then use a 10cm circle cutter to cut out circles of pastry. You should get 7 from each pastry sheet if you re-roll the trimmings.
Spoon 2 tsp of the mixture onto each. Snuggle a green olive in the middle, then brush half the border with egg. Fold over one half of the pastry, and seal by pinching the edge with your fingers, until you have 14 pasty shaped empanadas. Arrange on a baking parchment-lined tray, brush the rest of the egg over and scatter with sesame seeds. Chill for 30 minutes.
Preheat the oven to 200°C (180°C fan oven) Gas Mark 6 and bake for 20 minutes until golden and crisp.