To make the filling, place the beef in a large bowl, season, add the dried oregano and mix well.
Heat the oil in a large non-stick frying pan and cook the beef for 4-5 minutes turning occasionally until brown.
Add the onion, bacon or pancetta and garlic to the frying pan and cook for 2-3 minutes until the onion is soft but not brown. Add the tomato paste, wine or stock, chopped tomatoes and olives. Spoon into a small casserole dish and bring to the boil, reduce the heat and simmer for 1-2 hours, stirring occasionally.
Preheat the oven to 180°C/350°F/ Gas Mark 4. To prepare the filo pastry, brush the filo sheets with the melted butter and with a sharp knife cut into 60 x 6cm/ 2inch squares. Lightly grease 2 mini muffin tins and line each hole with three buttered filo squares, placing each one at a slightly different angle and gently press down.
Bake in the oven for 8-10 minutes until golden and crisp. Remove the tins from the oven and gently transfer the canapés to a metal cooling rack and set aside. Place the canapés on a serving platter, spoon about 2 teaspoons of the filling into each, garnish with the fresh oregano and serve immediately.