These hearty sandwiches are piled high with veggies—including earthy roasted beets and sweet potatoes, lemony arugula and quick-pickled onions—for a satisfying lunch or dinner. We use a whole-wheat baguette, but whole-wheat buns would work as well, if you prefer. Any color of beet would be delicious—try golden or Chioggia if you want to avoid the stains that red beets can leave.