Preheat the oven to 350 degrees F (175 degrees C).
Place chicken breasts on a baking sheet. Bake in the preheated oven until no longer pink and juices run clear, 20 to 30 minutes. Set aside.
Increase the oven temperature to 400 degrees F (200 degrees C).
Melt butter in a medium saucepan over medium heat. Stir in cream of mushroom soup, half-and-half, Parmesan cheese, garlic, lemon juice, and Italian seasoning, stirring constantly.
Arrange spinach in bottom of a 9x9-inch baking dish; cover with mushrooms. Pour ½ soup mixture over mushrooms; arrange chicken breasts on top. Cover with remaining soup mixture. Sprinkle with bacon bits; top with mozzarella cheese.
Bake in the preheated oven until bubbly and lightly browned, 20 to 25 minutes.
