In a mixing bowl, combine the drained tuna, mayonnaise, chopped red onion, dill pickles, minced parsley, minced dill, fresh lemon juice, salt, and black pepper. Gently mix until everything is well incorporated. Taste and adjust seasoning as needed.
On a clean surface, lay out your slices of bread. Spread a generous amount of the tuna salad mixture onto three slices. Top each with sliced tomatoes and a handful of shredded cheddar cheese or a slice of cheddar cheese.
Place the remaining slices of bread on top of the tuna salad and cheese. Spread softened butter on the outside of each sandwich to ensure a crispy, golden crust.
Heat a skillet or griddle over medium heat. Carefully place the sandwiches in the pan, buttered side down. Cook for about 4-5 minutes until golden brown. Flip the sandwiches and cook for another 4-5 minutes, pressing down gently with a spatula to help the cheese melt.
Once both sides are crispy and golden, remove the sandwiches from the skillet. Let them cool for a minute before cutting in half. Serve warm and enjoy every cheesy, flavorful bite!
