Place the panko in a shollow bowl or pie dish. Beat the egg to blend in another pie dish. Using a meat mallet or heavy rolling pin, gently flatten the swordfish steaks into 1/4 inch thickness. Sprinkle a swordfish steak with salt and pepper, then dip into the egg, allowing the excess to drip back into the bowl. Dredge the fish in the panko, coating it completely and patting lightly to adhere the crumbs onto the fish. Place the coated fish on a baking sheet and repeat with the reamining fish steaks.
Melt 1 tbsp. of butter with 1 tbsp of olive oil in a large saucepan over medium high heat. Add two crumb coated swordfish steaks and cook until brown and crisp and jsut cooked throughed, about 1 1/2 minutes per side. Transfer to a plate and tent with foil to keep warm. Wipe out the skillet, then repeat with the remaining butter, light oil, and swordfish steaks.
While the last 2 steaks are cooking, whisk the lemon juice and extra virgin olive oil ina large bowl to blend. Add the arugula and watercress, and toss to coat. Season the salad to taste with salt and pepper.
Top with the salad and serve.