Preheat oven to 375°.
In a large skillet, melt butter over medium heat then add onion.
Cook until softened then add garlic, stirring until fragrant.
Add crawfish and green onion and cook for about five minutes until heated.
Finally stir in cream cheese and Cajun seasoning until smooth and remove from heat.
In a bowl add mayo, mustard, and both shredded cheeses. Stir until smooth.
Add halved bread cut side up on a large baking sheet.
Spread mayo mixture on both bread halves.
Top each half with crawfish mixture, spreading to cover.
Sprinkle paprika all over the bread.
Bake until melted, about 15 minutes.
Turn oven to broil and brown for about 2 minutes.
Remove from oven and let cool slightly.
Sprinkle on parsley and slice and serve warm.