Halve swordfish steaks down center to make six 1/2-pound portions.
In a large, shallow glass-baking dish, combine yogurt, oil, chili paste, lemon juice, mint, and onion. Add fish and spread marinade over it. Cover with lid or plastic wrap and refrigerate 1 hour. (If you marinate fish longer, it "cooks" in marinade and becomes unpalatably mushy.)
Preheat the grill to high. Remove fish from refrigerator and allow to become room temperature. Drain off any excess marinade.
Oil cooking surface very lightly and grill fish (covered if on outdoor kettle grill) 5 to 7 minutes per side. Fish is done when slightly charred, opaque, and just beginning to flake.
Serve with lemon wedges, and pass olive oil to drizzle on top.