In a frying pan, melt a tablespoon of butter and sauté kale until soft. Set aside.
While pan is hot, add sliced baby bella mushrooms. If using fresh red peppers, add to the pan with the mushrooms. Sauté until soft. Set aside.
Use a pastry brush to butter one side of each slice of bread.
On the flip side of 2 slices of bread, portion horseradish and spread evenly.
Assemble each sandwich:
Lay one slice of bread butter side down, then top with 1-2 slices of Cooper® cheese. To each sandwich, add half the sautéed mushrooms, kale, and red peppers, then top with another 1-2 slices of Cooper® cheese. Place second slice of bread on top, butter side up.
Place sandwiches on a preheated griddle or frying pan. Grill until bread is golden brown, then carefully flip. Grill the other side of the sandwiches until golden brown and cheese is melted.
Remove from heat, serve, and enjoy!