Soak grilling planks in water for 1 hour. Drizzle steaks with oil. Combine the coriander, chili powder, allspice and cayenne; rub over both sides of steaks.
Grill, covered, over medium heat for 1-2 minutes on each side or until grill marks appear; remove.
Place planks on grill over direct medium heat. Cover and heat until planks create a light to medium smoke and begin to crackle (this indicates planks are ready), about 3 minutes. Turn planks over. Place steaks on planks.
Grill, covered, for 15-20 minutes or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°).
Top loin steak may be labeled as strip steak, Kansas City steak, New York strip steak, ambassador steak or boneless club steak in your region.