Preheat your oven to 400°F (200°C).
In a large skillet, melt the butter over medium heat. Once melted, whisk in the flour and cook for 1-2 minutes until bubbly and golden.
Gradually add the chicken broth and milk while whisking continuously to avoid lumps. Bring the mixture to a simmer and cook for 5 minutes until thickened.
Stir in the diced chicken, frozen peas and carrots, frozen corn, garlic powder, onion powder, dried thyme, salt, and pepper. Mix until well combined and heated through. Remove from heat.
In a mixing bowl, prepare the biscuit mix according to the package instructions, adding shredded cheddar cheese to the mix.
Pour the chicken mixture into an oven-safe baking dish, spreading it evenly.
Drop spoonfuls of the biscuit mixture over the top of the chicken filling, ensuring even coverage.
Bake in the preheated oven for 25-30 minutes, or until the biscuits are golden brown and cooked through.
Remove from the oven and allow to cool for a few minutes. Garnish with fresh parsley if desired before serving.