Thaw fish, if frozen. Arrange fish in a 2-quart square baking dish; set aside. In a small bowl whisk together lemon juice, oil, chili powder, cumin, salt, and pepper. Pour over fish. Turn fish to coat with marinade. Cover and chill for 15 minutes. Drain fish, discarding any marinade. Stack tortillas and wrap in foil.
For a charcoal grill, grill fish and tortillas on the greased rack of an uncovered grill directly over medium coals for 4 to 6 minutes or until fish flakes easily when tested with a fork and tortillas are warmed, turning tortilla stack once. (For a gas grill, preheat grill. Reduce heat to medium. Place fish and tortilla stack on greased grill rack over heat. Cover and grill as above.)
Transfer fish to a cutting board. Cut or flake fish into 1-inch pieces. Serve in warmed tortillas topped with Pineapple Salsa and/or Chipotle Coleslaw.