Turn all burners to high, cover, and heat grill until hot, about 10 to 15 minutes. Clean and oil cooking grate.
In a small bowl, whisk together dried basil, garlic powder, ground fennel, lemon pepper, cayenne pepper (if using), and salt and pepper to taste (I like 1 teaspoon salt and 1/2 teaspoon pepper).
Arrange swordfish on a baking sheet or plate. Drizzle with olive oil, then rub to coat. Sprinkle with the dry rub on all sides of the fish.
To make the olive topping, in a medium bowl add tomatoes, olives, fresh basil, garlic, lemon juice, olive oil, and salt and pepper to taste.
Grill the swordfish directly over high heat, turning once, until grill-marked, firm to the touch, and opaque throughout, 3-4 minutes on each side (the swordfish must hit 145 degrees on an instant thermometer). Serve with the olive topping.