Lightly grease the grates of an outdoor grill. Heat the grill to medium-high heat. Add the bratwurst to the grill and cook turning frequently until fully cooked (the internal temperature has reached 160 degrees F.) and browned on both sides.
Remove the bratwurst from the grill and allow it too cool. Once the bratwurst can be handled, slice it in half lengthwise.
Butter one side of each slice of the French bread. Take one of the bread slices butter side down and spread a layer of honey mustard onto the top. Place 1 slice of Muenster on top of the honey mustard.
Add two bratwurst halves strips over the cheese, and top with an additional slice of Muenster. Place the other bread slice over the cheese, butter side up. Repeat with a remaining sandwich.
Heat a large skillet or griddle to medium-high heat. Add the sandwiches to the skillet butter-side down.
Cook until the sandwiches are golden brown on the bottom (about 2 minutes). Turn and cook for another 2 minutes on the other side. Cook until golden brown and the cheese has melted.