To make sauce for the filling, heat oil in a pan. Add crushed garlic and sauté for 2 minutes. Add in the flour and stir until it turns slightly brown. Add the milk and stir well, making sure no lumps are formed. Simmer for 5-6 minutes, stirring in between.
Shred the boiled chicken with the help of a fork and add it to the sauce. Mix well. Add rolled oats, salt, fennel seed powder, black pepper, white pepper, garam masala powder and fried onion paste. Add the chicken stock. Cook for another 10 minutes, or until the desired consistency is reached, stirring occasionally.
Roll out the puff pastry sheet. For triangular patties (easier to make), divide it into six equal squares and brush with egg wash. Spread the filling on one half of each square, divided diagonally.
Fold the other half of each square. Brush with egg wash. Press the edges with a fork and make cuts on the face with a knife.
Bake in a pre-heated oven at 200°C for 20-25 minutes, or as stated on the puff pastry box.