Preheat oven to 300° F. Spray an 8 by 8-inch baking dish with cooking spray.
Combine butter, cream cheese, Mexican cheese, and milk in a medium saucepan. Heat over medium heat, stirring, until melted and combined. Add the corn, chilies, and half the green onions. Add salt and pepper to taste.
Pour mixture into prepared baking dish, sprinkle with the rest of the green onions, and bake for 30 minutes.