Preheat your oven to 400 degrees F.
Using a handheld mixer, beat cream cheese in a medium mixing bowl until smooth (medium to medium high speed).
Add mayonnaise, sour cream, HALF of the Parmesan cheese (¼ cup), cheddar cheese, horseradish, Cajun seasoning, garlic powder, pepper, hot sauce, and lemon juice. Beat until combined.
Gently stir in the crab meat using a large spoon.
Transfer mixture to a 1 quart baking dish and spread evenly.
Sprinkle evenly with the remaining Parmesan cheese.
Bake (uncovered) for 20 to 25 minutes, or until bubbly around the edges and heated through. If browning the top is desired, broil on high for 1 to 2 minutes (watch carefully while broiling!).
Cool for 10 to 15 minutes before serving to allow the crab dip to thicken.
Sprinkle with sliced green onions before serving.