To make tuna patties, you'll first need to prepare the ingredients. In a large bowl, whisk together the mayonnaise, mustard, Worcestershire sauce, salt, and pepper. Pour the mixture into the oiled skillet and cook over medium-high heat until the meat is no longer pink in the center. Remove the skillet from the heat and add the chopped onion. Cook the onion until it begins to soften, about 5 to 7 minutes. Add the cooked, crumbled romaine lettuce to the bowl and stir to combine. Season with salt and black pepper to taste. Heat the oil to medium high heat. Fry the bread slices until they're golden brown, 3 to 4 minutes per side. Set aside.