Preheat the oven to 425 degrees . In a food processor, pulse the swordfish until coarsely ground. Transfer to a medium bowl; add salt and pepper. Using your hands, mix in the egg and panko.
On a cutting board, make a gremolata by chopping together the parsley, lemon zest and garlic. Gently mix the gremolata, tomato, red onion and EVOO into the swordfish mixture.
Roll the swordfish mixture into walnut-size balls (about 2 tbsp. each) and arrange on a large rimmed baking sheet lined with parchment. Bake until the meatballs are cooked through and lightly browned in spots, about 15 minutes.
Squeeze the lemon wedges over the meatballs; serve with arugula salad.