The Must-Have Ingredient For Making Irresistible Tuna Melts

Tuna melts make for a delightful lunch that's easy to put together. Crispy toasted bread, creamy mayonnaise mixed with succulent canned tuna, all topped with oozing, melty cheese — what's not to love? As with most classic sandwiches, everyone's got their own way to prepare it. Yet, when we spoke with experts about the best tips for making irresistible tuna melts, they all seemed to agree on one thing: Don't skip the onion.

We love a finely diced red onion mixed in our tuna salad, which also brings a slight crunch, but you can also get away with shallots or sliced green onions. You can even opt to place rings of sliced red onion on top of the tuna mix when building the sandwich. Since there are so many different types of alliums that can be added in various ways, it's easy to customize a tuna melt recipe to suit everyone's taste.

Another way to amp up the flavor is with minced garlic, but not too much. The pungent, savory zing works beautifully with the rich flavor of tuna salad and melted cheese, as the acidity cuts through right where it's needed.

We've previously covered Ina Garten's unexpected tuna melt ingredient – along with Spanish tuna packed in olive oil, she adds a smidge of anchovy paste for an umami kick. The allium of her choice is chopped scallion, and she also throws in some fresh dill (which we highly recommend). Kamala Harris likes red onion in her tuna melt, as well as Dijon mustard and parsley.

If you prefer some real crunch in your tuna salad, diced celery plays well with raw onion, garlic, and most other inclusions. Finely diced pickle is a friend of onion and brings extra zing. As for cheeses, you can get as rich as you like, since raw onion is performing the flavor-balancing act. Aged cheddar melts beautifully and has robust flavor, and creamy Havarti is a top choice; or, to add even more complexity, try smoked Gouda or Applewood smoked cheddar. Just as long as you've got onion, you'll have an irresistible tuna melt.