Place the tuna in a fine mesh sieve and drain as much liquid from the tuna as possible.
4 – 5oz cans chunk white albacore tuna
In a medium size bowl combine the remaining tuna salad ingredients and stir to thoroughly combine.
⅔ cup mayonnaise, ¾ cup celery, ¼ cup (heaping) red onion, ¼ cup sweet pickle relish, 1 ½ tablespoon Dijon mustard, 1 teaspoon garlic powder, ½ teaspoon onion powder, ½ teaspoon kosher salt, ¼ teaspoon black pepper
Add in the drained tuna and fold it into the mayo mixture until combined.
Heat a skillet over medium low heat. Butter two slices of bread on one side. Scoop the tuna salad on one piece of bread (on the unbuttered side), then top with a slice or two of cheese. Top with other buttered slice of bread.
Place in hot skillet, buttered side down. Grill until golden, flip and grill until other side is golden and the cheese is melty.