Preheat your oven: Begin by preheating your oven to 375°F.
Prepare the bread: Cut the 12-ounce loaf of French bread in half lengthwise. Spread ½ cup of mayonnaise evenly on both halves, ensuring a consistent layer.
Sauté the onions: In a skillet, melt 2 tablespoons of butter over medium heat. Add the ¾ cup of finely chopped sweet onion and sauté until softened, about 5 minutes. Stir in 3 cloves of minced garlic and cook until fragrant, around 1 minute.
Add the crawfish: Mix in 1 pound of cooked crawfish tails, ¾ cup of chopped green onion, and 1 tablespoon of chopped fresh parsley. Stir everything together and heat until warmed through, which should take about 3-4 minutes.
Prepare the cream mixture: In a bowl, combine 1 teaspoon of Cajun seasoning with 1 (8-ounce) package of softened cream cheese. Mix until you achieve a smooth consistency.
Spread the mixture: Take the crawfish mixture off the heat and spread it evenly over the prepared bread halves. Then, sprinkle with ½ cup grated Parmesan cheese, ¾ cup shredded Monterey Jack cheese with peppers, and finish with ½ teaspoon sweet paprika.
Bake: Place the prepared bread onto a baking sheet and bake for about 15 minutes. To achieve a golden finish, broil for an additional 2 minutes, keeping a close eye to prevent burning.
Garnish and serve: Once out of the oven, garnish with extra parsley if desired. Serve warm, and enjoy!