Slice French bread loaf lengthwise into halves, then scoop out the inside of the loaf. Set aside.

In a large skillet, melt butter over medium-high heat. Sauté the onion, bell pepper, celery, and garlic for 5-7 minutes. Add the crawfish tails, paprika, cayenne, and sauté for 3 more minutes.

Lower the heat, then stir in mustard and mayonnaise. Add the cheeses and stir until melted. Remove from heat.

Spread mixture inside the bread then put halves back together. Butter the top of the loaf, wrap it in foil and bake on a hot grill or in a 350°F oven for 20 to 30 minutes.

Remove the bread from the oven or grill, cut into slices and serve while hot.