Notes: If using firm, crusty, coarse-textured bread such as ciabatta or pane francese, you can make the sandwiches at home up to 4 hours ahead; cover and chill. Otherwise, transport bread, arugula, cheese, and marinated vegetables separately, and let everyone assemble their own sandwiches on-site.
1 loaf (1 lb.) herb-flavor or plain focaccia, ciabatta, or pane francese bread (1 to 1 1/2 in. thick)
1 to 2 ounces arugula or watercress sprigs, rinsed and crisped
Cut focaccia into 4 equal pieces, then split each piece in half horizontally.
Lay arugula evenly over cut sides of focaccia bottoms. Arrange cheese slices evenly over arugula. Top equally with grilled vegetables and moisten with some of the marinade. Add salt and pepper to taste, and cover with focaccia tops.