Roasting turns a so-so tomato into something pretty tasty, but it makes a high-season beauty that much more amazing. Here, the tomatoes can be roasted ahead of time so you can avoid having your oven on during the afternoon heat.
04Sprinkle each steak all over with 1/4 teaspoon salt and 1/4 teaspoon pepper (total per steak). Oil grill rack, then grill steaks, covered only if using a gas grill, turning over once, 5 to 6 minutes total for medium-rare. Transfer to a cutting board.
05Lightly brush both sides of bread slices with some of oil from roasted tomatoes and grill, covered only if using a gas grill, turning over once, until lightly toasted and grill marks form, about 1 minute total. Stir together vinegar and sugar until sugar is dissolved, then stir in herbs. Spread one side of each bread slice with some of herb mixture (about a tablespoon per slice). Slice steaks, then make into sandwiches with bread, roasted tomatoes and shallots, and watercress.