Spread dressing on both slices of bread; set aside.

Mist a large nonstick pan with cooking spray and set over medium-high heat. Add corned beef to pan and warm through, about 1 1/2 minutes. Move meat to one side of pan; add sauerkraut to pan and stir it until heated through, about 2 minutes. Remove pan from heat and transfer corned beef and sauerkraut to a plate; cover and set aside.

Lightly mist same pan with cooking spray and place over medium heat. Place 1 slice of bread, dressing side up, in pan; top bread with corned beef and then layer with sauerkraut and cheese.

Carefully place remaining slice of bread, dressing side down, on top; gently press down with a spatula for about 2 minutes. Flip sandwich and heat for 2 minutes more; remove from heat promptly.