Add zest 1 lime and the juice of 1/2 lime into a bowl. Add olive oil and mix until just emulsified. Add diced onion and jalapeno, meanwhile chop mango into small cubes, and finely chop cilantro. Combine all ingredients and season with salt and pepper to taste. Cover and refrigerate until fish is cooked.
For the fish: Heat pan on medium high heat. Make sure the pan is big enough for both pieces without crowding. Liberally season all sides of fish with salt and fresh cracked pepper. Sprinkle 1/4 teaspoon cayenne pepper to both sides. When pan is hot enough, add olive oil then the swordfish. Cook 3-4 minutes per side flipping only once. When fish is done, top with mango salsa. Serve with a lime wedge if so desired.