Heat gas or charcoal grill. In medium bowl, mix avocado, cilantro and dressing. Set aside. Heat taco shells as directed on package.
In large bowl, mix oil, lemon-pepper seasoning, chili powder and salt. Add halibut; toss gently to coat. Place halibut in grill basket. Place basket on grill over medium heat. Cover grill; cook 5 to 10 minutes or until fish flakes easily with fork, rearranging twice. Fill taco shells with fish, lettuce, avocado mixture and tomato.