Step 1: Prepare the Tuna Salad : In a medium bowl, combine drained tuna, mayonnaise, mustard, celery, onion, pickle, lemon juice, salt, and pepper. Mix well until all ingredients are evenly coated and creamy. Adjust seasoning to taste. Set aside while you prepare the bread and cheese.
Step 2: Assemble the Sandwich : Lay out the bread slices on a clean surface. Spread butter on one side of each slice — this will be the outer side for grilling. On the unbuttered side, spread a generous layer of the tuna mixture. Top with shredded or sliced cheddar cheese, then close the sandwich with another slice of bread (buttered side out).
Step 3: Grill the Sandwich : Heat a large nonstick skillet or griddle over medium heat. Place the sandwiches in the skillet (2 at a time if needed). Grill for 3–4 minutes per side, pressing lightly with a spatula until the bread is golden brown and crisp and the cheese has melted. Remove from the skillet, let rest for 1–2 minutes, then slice in half.
Step 4: Serve and Enjoy : Srve hot, with the cheese perfectly melted and the bread crisp to perfection. Pair with soup, salad, or fries for a complete meal.