Preheat the oven to 375°F.
In a large skillet, melt the butter over medium heat. Add the diced onion and celery, cooking until softened, about 5 minutes.
Stir in the flour and cook for an additional minute.
Gradually whisk in the chicken broth and milk, stirring constantly until the mixture thickens, about 5-7 minutes.
Add the shredded chicken, frozen vegetables, garlic powder, onion powder, thyme, salt, and pepper. Mix well and remove from heat.
Pour the chicken mixture into a 9x13-inch baking dish.
Open the biscuit dough and separate the biscuits. Arrange the biscuits on top of the chicken mixture, leaving some space between each.
Bake in the preheated oven for 25-30 minutes, or until the biscuits are golden brown and cooked through.
Let cool for 5 minutes before serving.