Nothing wrong with looking forward to lunch – even if you haven't left the house yet.
Medium-rare roast beef slices
Sharp horseradish cheddar
When making the sandwich spread the Dijon on both side of a fresh Italian bun. Divide your medium-rare roast beef slices (leftovers are perfect or buy the good stuff at the deli) between both sides before adding the final ingredients. That way you prevent the bun from getting soggy from the other condiments.