Drain canned tuna thoroughly — press firmly in a strainer or squeeze in a paper towel to remove as much liquid as possible. Excess moisture prevents browning. Mix drained tuna with mayo, lemon juice, salt, pepper, and any mix-ins like celery, pickles, or red onion. If making a sandwich melt, butter one side of each bread slice and set aside. Slice your cheese and have everything ready before the skillet heats up — cook time moves fast.

Preheat a nonstick skillet over medium heat for about 1 minute. Medium heat is key — too high burns the bread before the cheese melts, too low gives soggy results. For a tuna melt sandwich: Assemble with tuna on the unbuttered side of the bread, add tomato slices if using, then layer on two slices of cheese. Top with the second slice buttered side up. Place in the skillet cheese side down. Cook undisturbed 3 to 4 minutes until deep golden brown on the bottom. Flip and cook another 3 to 4 minutes until the second side is golden and cheese is fully melted. Total cook time is 4 to 8 minutes depending on pan, heat, and bread thickness. For loose tuna without bread: Add tuna mixture directly to the preheated skillet over medium heat. Stir and cook about 5 minutes until heated through and moisture has cooked off, stirring occasionally to prevent sticking.

Look for uniformly golden brown bread on both sides and cheese that is visibly melted with slight bubbling at the edges. If bread browns too fast before cheese melts, lower the heat. For loose skillet tuna, cook at medium heat until the mixture is heated through and no longer looks wet or cold in the center, about 5 minutes. Serve immediately while cheese is still molten. Avoid: under-draining tuna (causes steaming instead of a proper melt), heat too high (burns bread before interior heats), and skipping butter on the bread (butter creates the golden crust). Serve warm with pickles and chips.