Preheat your oven to 400°F (200°C).
In a large saucepan, heat olive oil over medium heat. Add onion, carrots, celery, and cook until softened, about 5 minutes.
Stir in cooked chicken, peas, corn, garlic powder, thyme, salt, and pepper. Mix well.
Sprinkle flour over the mixture, stirring to combine. Cook for another 2 minutes to eliminate the raw flour taste.
Gradually add chicken broth and heavy cream, stirring constantly until the mixture thickens (about 5-7 minutes).
Transfer the filling to a baking dish, spreading it evenly.
In a mixing bowl, combine flour, baking powder, garlic powder, and salt for the biscuit topping. Cut in cold butter until the mixture resembles coarse crumbs.
Stir in shredded cheddar cheese, then add milk, mixing until just combined.
Drop spoonfuls of the biscuit dough over the chicken pot pie filling.
Bake in the preheated oven for 25-30 minutes, or until the biscuits are golden brown and the filling is bubbly.
Allow to cool for a few minutes before serving.