In a large pot of boiling salted water, cook pasta 3 minutes less than package instructions.
Meanwhile, in a large saucepan, melt butter over medium-high heat. Add onion, celery, seasoning, and salt, and cook until onion is translucent, about 4 minutes. Add flour and cook, stirring, 1 minute. Gradually add broth, stirring constantly, then bring to a boil. Reduce heat and simmer 5 minutes, stirring throughout.
Add the mixed vegetables and cooked chicken, and combine with sauce.
Drain pasta and add to skillet, toss to combine.
Notes
Make this gluten-free by using 1:1gluten-free all-purpose flour and gluten-free pasta. Don’t have poultry seasoning? Substitute it with ½ teaspoon ground cumin and ¼ teaspoon ground chili in this recipe.