Butter or spray with cooking spray a 8x8 inch deep baking dish and set aside.
With your hands, shred the chicken into tiny pieces and place onto the bottom of the baking dish. Top with 1/2 cup Caesar dressing. The dressing won't cover the chicken entirely, so just scoop it over the chicken.
In a large mixing bowl combine shredded American cheese, shredded parmesan cheese, cream cheese and 1 cup of Caesar dressing. Using a hand mixer, mix until all fully combined.
Top the chicken with the cheese mixture. Level the top.
Bake for 25-30 minutes, until the top is golden brown and bubbly. After 25 minutes of baking, you can turn on the broiler for 2 minutes, for a crispier top. Watch carefully not to burn the cheese!
Top with the remaining parmesan cheese and chopped green onions.