Creating the perfect Tuna Melt is simple when you follow these easy steps:

1. Prepare the Tuna Mixture: In a medium bowl, combine the drained tuna, mayonnaise, Dijon mustard (if using), diced celery, garlic powder, salt, and pepper. Mix well until all ingredients are evenly distributed.
2. Assemble the Sandwich: Take two slices of bread and place a generous amount of the tuna mixture on each. Top with a handful of shredded cheese.
3. Close the Sandwich: Place the remaining two slices of bread on top to create two sandwiches.
4. Preheat the Pan: Heat a skillet over medium heat. Add a little butter or margarine to coat the pan.
5. Grill the Sandwiches: Once the pan is hot, place the sandwiches in the skillet. Grill for about 3-4 minutes, or until the bottom is golden brown and crispy.
6. Flip and Cook: Carefully flip the sandwiches and add more butter to the pan if needed. Grill for another 3-4 minutes, until the other side is golden and the cheese has melted.
7. Remove and Slice: Once cooked, remove the sandwiches from the skillet. Allow them to cool slightly before cutting them in half.
8. Serve Warm: Serve the Tuna Melt warm, perhaps with a side of chips or a fresh salad.

These straightforward steps will guide you in making a delightful Tuna Melt that is sure to satisfy your cravings!