Dice the chicken into small, bite-sized pieces and season lightly with salt, pepper, thyme, and garlic powder.
Pour the cream of chicken soup into the crockpot and add the chicken broth, stirring until smooth and combined.
Add the diced chicken and frozen vegetables to the crockpot, stirring well to coat everything evenly in the creamy mixture.
Cover and cook on low for about 4 hours, until the chicken is tender and flavors meld together, filling your kitchen with a savory aroma.
About 30 minutes before serving, preheat your oven to 200°C (400°F). Transfer the hot filling to a baking dish and lay the puff pastry or pie crust on top, trimming off any excess.
Brush the pastry with a little egg wash or milk for a shiny finish, then bake in the oven for 20-25 minutes, until golden brown and crisp on top.
Remove from the oven and let rest for 5 minutes. If you prefer, stir in a splash of milk or cream into the filling for extra richness.
Slice or scoop the bubbling, flaky-topped pie onto plates. Garnish with fresh herbs if desired and serve hot for a comforting, hearty meal.