1 (9.25-ounce) can tuna, drained
2/3 cup mayonnaise
1/4 cup prepared horseradish (or to taste)
1 stalk celery, diced
2 tablespoons freshly grated Parmesan cheese
2 tablespoons onion, chopped fine
2 tablespoons sweet pickle relish
Mix all ingredients together. Cover and refrigerate for one hour. Serve in a tomato cup or on buns with lettuce and tomato slices.