These are both a snack and a flashy hors d'oeuvre to get a party going. The almonds, horseradish and mustard link up beautifully and bring out the tastiest aspects of the roast beef. Want to make it extra spicy? Add a few drops of hot sauce to the horseradish. Everything comes to the recipe fairly well seasoned as-is, but add some salt if you like.
Make the horseradish mix: In a large bowl, whisk together the cream cheese, horseradish sauce, and mustard.
Assemble the tortillas: Spread each tortilla with about 3 tablespoons horseradish mixture. Arrange about 1/4 cup of the arugula evenly over the horseradish. Layer3-4 slices of roast beef on top. Sprinkle with 1/4 cup cheddar cheese and about 2 generous tablespoons almonds. Starting at one end, gently roll up each tortilla into a tight tube. Wrap in plastic to keep rolls tight. Refrigerate until chilled.
Serve: Trim the ends off of the rolls and slice each roll into 8 rounds. Arrange on a platter to serve.