In a bowl, mix the tuna with the olive oil, fresh herbs, salt and pepper. Stir until combined. You can also just buy the tuna packed in olive oil, but I like having a little more control over the oil situation!
To make the sun dried tomato spread, drain the tomatoes from the olive oil in the jar. Add the tomatoes to a food processor and blend until pureed.
To make the sandwiches, spread a tablespoon of the tomatoes on one (or both!) sides of the bread. Heat a large skillet over medium heat. Spread the outsides of the bread with softened butter. Assemble the rest of the sandwich by adding 1 or 2 slices of cheese, a scoop of the tuna, a few pickled onions and a handful of arugula on one slice. Cover it with the other slice of bread.
Cook the sandwich in the skillet until the cheese is melted and bubbly and the bread is golden brown. Serve immediately!