Combine all of the ingredients except for sourdough, butter and cheddar cheese in a bowl to make the tuna salad.
Heat your large skillet or griddle to medium heat.
Butter one side of all of the sourdough bread.
Once your griddle is hot, add sourdough buttered side down, top with one slice of cheese, a quarter of the tuna salad, another slice of cheddar and then top with final slice of sourdough buttered side up.
Gently press down sandwich with spatula. Let cook for a few minutes until golden on the bottom, then carefully flip sandwich over with spatula and let cook for another few minutes until golden and cheeses are melted.
Remove sandwiches from the skillet and serve with your favorite side dishes. Enjoy!