Roast beef and horseradish sandwich

Name: Roast beef and horseradish sandwich
Prep time: 5 min
Total time: 5 min
Yield: 1 servings
Cuisine: British
Ingredients: 60 gr of Cooked roast beef slices; 1 Crusty bread roll; 1 tbsp of Horseradish sauce; 1 slice of Unsalted butter; 1 handful of Wild rocket