Preheat and prep: Preheat the oven to 375°F. Spray an 11x7 casserole dish with cooking spray. Set aside.
Cube chicken: Cut 1 1/2 pounds of chicken breast into 1 inch cubes and scatter throughout the baking dish. Sprinkle with salt and pepper.
Mix sauce ingredients: In a small bowl, mix together 1 can cream of celery soup, 1 can cream of chicken soup, 1/4 cup milk, and 1/2 teaspoon Italian seasoning. Stir until smooth. Stir in 1 cup frozen mixed vegetables.
Spread sauce: Pour the sauce over the chicken and spread it so the chicken is covered.
Add stuffing: Sprinkle one box of dry stuffing over the top.
Pour chicken broth: Drizzle 1 cup chicken broth over the stuffing, trying to moisten most of the stuffing.
Bake: Cover with foil and bake for 40 minutes. Take foil off and bake another 5 minutes.
Notes
Storage: Store leftovers in an airtight container in the fridge up to 3 days.