Preheat your oven to 400°F (200°C). Grease a 9x13-inch baking dish with cooking spray or butter.
In a large bowl, combine the shredded chicken, frozen mixed vegetables, chicken broth, 1 cup of milk, garlic powder, onion powder, thyme, salt, and black pepper. Stir until well mixed and pour the mixture into the prepared baking dish.
In another bowl, whisk together the flour, baking powder, and ½ teaspoon of salt. Add the melted butter and ¾ cup of milk to the dry ingredients, stirring until just combined. The batter will be thick.
Drop spoonfuls of the batter over the chicken mixture in the baking dish, covering as much of the surface as possible.
Bake in the preheated oven for 30-35 minutes, or until the top is golden brown and a toothpick inserted into the batter comes out clean.
Let it cool for about 5 minutes before serving.