1 pound mock crab meat, cut into slices
2 tablespoons fresh lime juice, or to taste
1/2 cup mayonnaise
2 teaspoons coarse-grained mustard
four 1-inch-thick slices brioche or challah
unsalted butter, softened, if desired
4 tablespoons freshly grated Parmesan
Put the mock crab in a bowl but do not shred. Add 1 tablespoon lime juice and toss to combine. In a small bowl whisk together remaining tablespoon lime juice, mayonnaise, and mustard until smooth. Pour sauce over mock crab and toss to coat. Season mock crab mixture with salt and pepper and chill, covered, 30 minutes. Lightly toast brioche or challah. Lightly butter toast. Spoon one fourth mock crab mixture into a 1/2-cup measure. Invert mock crab onto bread, spread to reach the sides of the bread and set it on an ungreased baking sheet. Repeat procedure with remaining mock crab mixture and bread. Sprinkle 1 tablespoon Parmesan over each sandwich. Broil sandwiches about 3 inches from heat until cheese is melted and golden, 1 to 2 minutes.