Preheat the oven to 375°F (190°C) and lightly grease a cast iron pan or ovenproof skillet with nonstick spray.
Pat the 4 chicken breasts dry with paper towels and season both sides with salt, pepper, and poultry seasoning.
Place the seasoned chicken breasts in the prepared skillet in a single layer.
Spread about 14 oz prepared spinach dip evenly over the top of each chicken breast.
Sprinkle 1 cup shredded mozzarella evenly over the spinach-topped chicken.
Bake in the preheated oven for about 30 minutes, or until an instant-read thermometer inserted into the thickest part registers 165°F (74°C).
Switch the oven to broil and broil for 3–5 minutes, watching closely, until the cheese is golden and bubbly.
Remove the pan from the oven and let the chicken rest for 5 minutes before serving.