Crab Cake Sandwiches for a Crowd

Name: Crab Cake Sandwiches for a Crowd
Ingredients: One 12-ounce package soft brioche baguette or sub rolls; 5 tablespoons unsalted butter, melted; 2/3 cup mayonnaise; 1/4 cup chopped fresh parsley; 1 tablespoon finely grated lemon zest plus 2 tablespoons lemon juice (from about 1 lemon); 1 tablespoon Dijon mustard; 2 teaspoons seafood seasoning, such as Old Bay; 2 scallions, thinly sliced; 1 tablespoon ketchup; 2 pinches cayenne pepper, or to taste; 1 1/2 pounds jumbo lump or lump crab meat, picked through for cartilage and shells; 1/2 cup plain breadcrumbs; Kosher salt and freshly ground black pepper; 2 plum tomatoes, thinly sliced; 1 small head Bibb lettuce, separated into leaves