Bring 4 quarts of salted water to a boil. Add gluten-free pasta, cook slightly under al dente per package instructions, then drain and set aside.
Meanwhile, heat butter in a large pot over medium heat. Sauté onion, carrots, and garlic until tender.
Add diced chicken and cook until no longer pink.
Sprinkle gluten-free flour over the mixture, stirring constantly for 2 minutes to cook out raw taste.
Gradually pour in chicken broth and milk, whisking until smooth and simmering until thickened.
Stir in peas, corn, thyme, and garlic powder. Season with salt and pepper.
Return cooked pasta to pot and simmer 5-7 minutes until pasta is tender and sauce coats the mixture.
Serve warm, garnished with fresh herbs if desired.