In a large skillet (one wide enough to hold swordfish in a single layer), heat oil over medium-high heat.
Add onion and garlic; cook, stirring frequently, until onion is lightly browned, 3 to 4 minutes. Remove from heat.
Add sun-dried tomatoes, olives, capers, wine and generous pinch red pepper flakes; stir together. Transfer to bowl.
Lightly season swordfish with salt and pepper; in a single layer, place fish in skillet.
Return skillet to medium-high heat, cover and cook for 3 minutes per side.
When swordfish is cooked through and browned, cover with sauce and warm.
Sprinkle roughly torn basil and serve. This dish can also be served room temperature.