Heat oven to 375°F. Line a sheet pan with foil.
Split the bread and place cut-sides up on the pan. Bake 5–7 minutes to lightly toast.
Melt butter in a large skillet over medium heat. Soften onion, bell pepper, and celery for 5–6 minutes.
Stir in garlic and cook 30 seconds. Fold in crawfish, Creole seasoning, paprika, cayenne, salt, and pepper; warm 2 minutes.
Splash in lemon juice and hot sauce. Remove from heat and let cool 3–5 minutes.
Beat cream cheese with mayonnaise in a bowl until smooth. Mix in the crawfish mixture, green onions, parsley, and half the cheeses.
Mound filling onto the toasted bread. Sprinkle with the remaining cheeses.
Bake until hot and bubbly, 10–12 minutes. Broil 1–2 minutes for extra browning if desired.
Rest 5 minutes. Slice into pieces and serve warm.