We topped them with spicy brown mustard, red onion, cherry tomatoes and avocado and served on lettuce. (marthastewart.com)
I added spicy brown mustard to mine - this was so good! (mybizzykitchen.com)
Create a tasty dish by mixing tuna with a generous portion of chopped pickles, a tablespoon of balsamic vinegar, half a teaspoon of dried Italian herb seasoning, plus a teaspoon of spicy brown mustard, and lemon juice. (health.com)