Preheat your oven to 400°F.
In a large mixing bowl, combine the cooked chicken, frozen mixed vegetables, chicken broth, milk, garlic powder, onion powder, thyme, salt, and pepper. Stir until well mixed.
In another bowl, whisk together the flour, baking powder, and baking soda. Add the melted butter and egg to the dry ingredients, mixing until just combined.
Pour the chicken mixture into a greased 9x13 inch baking dish.
Drop spoonfuls of the batter over the chicken mixture, spreading it out as evenly as possible.
Sprinkle the shredded cheddar cheese on top.
Bake in the preheated oven for 25-30 minutes, or until the batter is golden brown and cooked through.
Let it cool for about 5 minutes before serving.