Preheat oven to 375°F (190°C). Cut the French bread lengthwise and spread a thin layer of mayo on the cut side of each half.

In a skillet, melt a small amount of butter over medium heat. Add the Trinity mix (onion, bell pepper, and celery), green onions, and minced garlic. Sauté for about 10 minutes until softened.

Add the crawfish to the skillet and cook for a few minutes with the vegetable mixture. Then, add the cream cheese, pepper jack cheese, Parmesan cheese, Cajun seasoning, and granulated garlic. Let the mixture come to a simmer and cook for 15 minutes, stirring occasionally.

Spread the crawfish mixture evenly over the mayo-coated French bread halves. Sprinkle with additional Parmesan cheese.

Place in the preheated oven and bake for about 15 minutes, or until the bread is golden and the cheese is bubbly.

Slice and serve warm as an appetizer.