Steak-and-Mushroom Reubens

Heat oil in large nonstick skillet over medium-high heat. Sprinkle 1 1/2 teaspoons pickling spice on each side of steak, then sprinkle both sides with salt and pepper. Add steak to skillet and cook to medium rare, about 4 minutes per side. Transfer to cutting board. Add mushrooms to same skillet. Cover and cook until mushrooms are tender, turning occasionally, about 3 minutes. Transfer mushrooms to bowl. Thinly slice steak on diagonal. Arrange 6 bread slices on work surface. Spread with dressing. Layer each with steak, 2 mushroom caps, sauerkraut, and cheese. Top with remaining bread slices. Spray 2 large nonstick skillets with nonstick spray. Add sandwiches to skillets; place over medium heat. Cover and cook until bottoms are golden, about 3 minutes. Remove skillets from heat. Remove sandwiches. Spray skillets with nonstick spray. Turn sandwiches over into skillets. Cover and cook until bottoms are golden and cheese is melted, 2 to 3 minutes.