In a large skillet (medium heat), put the olive oil, onion, garlic. Let it cook until the onion is golden and soft. Add the beef, salt and pepper and let it fry for a few minutes in high-medium heat. As soon as the beef loses its pink/red color, add the lemon juice and bring the heat to a medium-low. Leave it cooking, stirring occasionally, for 7 minutes. Let the meat cool off.
Next, take the puff pastry sheets and cut them into rectangle-shaped pieces (each sheet can be cut into 4-5 rectangles). Put a teaspoon-full of the meat on one of the sides of the the rectangle. Then take the other side and fold it over. This makes one tiny cake. Keep doing making the cakes until you run out of pastry.
Put the cakes in the oven for the amount of time it says on the puff pastry package (12-17 minutes).