In a bowl, mix the tuna, mayo, Dijon, soy sauce, Worcestershire, pickles, celery, green onion and black pepper. Stir until well combined.
On a stovetop, heat skillet to medium.
Spread butter or mayo on one side of each slice of bread (this will be the outside). On the unbuttered side, layer shredded cheddar, a generous scoop of tuna salad, more cheese and the other slice of bread.
Cook sandwiches butter-side down until golden and crispy, about 3–4 minutes per side, pressing gently with a spatula.
Flip and repeat until the bread is toasted and the cheese is melted. Slice in half and serve.