Ingredients

• 6 tablespoons mayonnaise
• 2 6-ounce cans solid white tuna, drained
• 1/4 cup finely chopped celery
• 2 scallions, finely chopped
• 2 tablespoons finely chopped fresh parsley
• 2 teaspoons apple cider vinegar
• Kosher salt and freshly ground pepper
• 1 tablespoon whole-grain mustard
• 1 tablespoon prepared horseradish
• 4 large slices rye bread, lightly toasted
• 8 thin slices havarti cheese
• 2 tomatoes, cut into 8 slices
• Dill pickles, for serving (optional)

Instructions

1. Position a rack in the upper third of the oven and preheat to 475 degrees F. Combine 4 tablespoons mayonnaise, the tuna, celery, scallions, parsley and vinegar in a large bowl and mix well. Season with salt and pepper.
2. Combine the remaining 2 tablespoons mayonnaise with the mustard and horseradish in a small bowl; spread on the bread slices and arrange on a baking sheet. Mound the tuna mixture on top and pat it into an even layer. Top each with 1 cheese slice, tearing it as needed to cover the tuna mixture.
3. Season the tomato slices with salt; place 2 slices on top of each sandwich, then top each with another cheese slice. Bake until the cheese melts, 5 to 7 minutes. Serve with dill pickles.