In a large bowl, combine the ground beef, chopped parsley, finely chopped garlic, Worcestershire sauce, and Montreal-style steak seasoning. Mix well until just combined. Shape into 3 equal patties, about ¾-inch thick.

Heat a nonstick griddle or skillet over medium heat. Cook the patties for 4-6 minutes on each side, checking for an internal temperature of 160°F (71°C). Remove from heat and set aside.

Warm the griddle again. Place buttered slices of bread on the griddle, butter-side down. Layer with a slice of cheese, a cooked patty, another slice of cheese, and top with the remaining slices of bread, butter-side up.

Grill the sandwiches for 3-5 minutes until golden brown, then flip and cook the other side for an additional 3-5 minutes until the cheese is melted.

Remove from heat, let rest for a minute, slice in half, and serve warm with your favorite sides.