Step 2
Melt butter in a large Dutch oven over medium. Add onion and cook, stirring often, until tender, about 5 minutes. Stir in flour, thyme, mustard, garlic powder, onion powder, salt, and pepper; cook, stirring constantly, 1 minute. Gradually stir milk and broth into flour mixture; cook, stirring constantly, until bubbling and thickened, 3 to 5 minutes. Stir in chicken, vegetables, and parsley. Remove from heat, and cover to keep warm.