In a bowl, stir together the thyme, garlic powder, 4 tablespoons of the cayenne, 3 tablespoons of the seafood seasoning and 2 tablespoons salt. Slice the tuna and coat on both sides with the spice mixture. Set aside to let the spices soak in.
Place the egg whites in a blender and add the cream of tartar, vinegar, mustard, lemon juice, 3 tablespoons of the brown sugar and the remaining 2 tablespoons seafood seasoning. Blend at high speed while slowly pouring in the oil. Once thickened, add the pickles and the remaining 4 tablespoons cayenne and blend. Place in a bowl, cover and chill.
Add the butter to a large skillet and melt over medium heat. Add the onions, Worcestershire and the remaining 2 tablespoons brown sugar and cook, stirring occasionally, until the onions are slightly wilted down.
Prepare a grill or grill pan for cooking over medium-high heat and preheat the oven to 400 degrees F.
Spread the Creole mayo remoulade on the bread slices.
Lightly oil the grill grates. Grill the tuna for 1 minute per side, then remove to a baking sheet. Layer the Jack cheese and Swiss cheese on 4 of the bread slices, over the remoulade, and top with the cooked onions. Arrange the tuna on top of the onions, then close the bread to make sandwiches. Bake the sandwiches to melt the cheese, 8 minutes. Serve immediately.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.