Get a pan on medium-high heat.
Drizzle your tuna steak with olive oil, salt & pepper to taste.
Once pan is heated, sear tuna for about one and a half minutes on each side.
Remove tuna, turn heat to medium-low.
Butter the outside of each slice of bread.
On bottom slice, spread about a tablespoon of mayo.
Place gruyere cheese, dill pickle, celery, green onion, and fresh dill.
Place sliced tuna on top along with more fresh dill and cheddar cheese.
Spread about a tablespoon of mayo on inside of top slice.
Place your sandwich in the pan, cover with lid, and turn to medium heat.
Fry until golden brown on each side.