Press pepper evenly onto all surfaces of the pot roast. Heat oil in stockpot over medium heat until hot. Place pot roast in stockpot; brown evenly. Pour off drippings.
Add onion, water, Worcestershire sauce and 2 tablespoons horseradish. Return beef to stockpot; bring to a boil. Reduce heat; cover tightly and simmer 2 hours and 15 minutes to 2 hours and 30 minutes, or until pot roast is fork-tender.
Meanwhile, prepare barley according to package directions for 6 servings. Remove from heat. Stir in kale. Cover; let stand 5 minutes.
Remove beef; keep warm. Skim fat from cooking liquid, if necessary; bring to boil. Reduce heat to medium and cook 10 to 13 minutes or until reduced to 1-1/2 cups, stirring occasionally. Stir in remaining 1 teaspoon horseradish.
Carve pot roast into thin slices. Return beef to cooking liquid and heat through. Serve beef over barley mixture.
