Place chicken breasts, onion, and poultry seasoning in a medium saucepan and add enough water to cover.
Step 4
Simmer over medium heat for 8 to 10 minutes, until chicken is cooked through. Drain and dice chicken
Step 5
In a large bowl, combine chicken, onions, cream of chicken soup, cream of mushroom soup, cheddar cheese, mozzarella cheese, mixed vegetables, mushrooms, salt and pepper. Mix thoroughly.
Step 6
Lay one sheet of pastry in bottom of pan. Pour chicken mixture over pastry. Cover with second sheet and seal. Cut steam vents in top.
Step 7
Bake in preheated oven for 50 minutes, until pastry is golden brown.