Preheat oven to 400 degrees.

In a large pot, heat the oil over medium heat. Add the onion and mushrooms and saute until translucent and softened, about 3-4 minutes.

Add the flour, garlic powder, Italian seasoning, salt, and pepper. Stir continuously for about 30 seconds, then whisk in the chicken broth and milk until no clumps of flour remain. Bring to a simmer, and simmer for 5 minutes or until thickened.

Add the frozen vegetables and chicken and stir. Remove from heat.

Lay each sheet of puff pastry out on a cutting board and cut into 12 rectangles (6 rectangles per sheet).

Generously grease a muffin tin, then place the puff pastry pieces in each muffin well. Fill with pot pie filling. Bring the corners together slightly, then brush the edges with egg wash.

Bake in the oven for 22-23 minutes, or until golden brown. Serve!