Cook the mushrooms. Heat a little olive oil or butter in the pan, add the mushroom slices and cook over a medium-high heat until the mushrooms start to release their juices. Drizzle the balsamic over the top and add the garlic to the pan, then cook until the liquid is all evaporated from the pan and the mushrooms are reduced and browning.
Butter a slice of bread and place it down on a plate, butter side down. Pile on half the cheese, then the mushrooms. Drizzle the hot honey over the mushrooms.
Wipe out of your frying pan and bring it back to a medium heat. Place the sandwich in the frying pan and allow it to cook while gently pressing down with a spatula.
Once you see cheese melting on the lower side, flip it over, and continue to cook until the cheese has melted throughout and the bread has turned crispy brown.
