Heat a grill pan over medium-high heat 5 minutes. As pan heats, peel pineapple half; cut lengthwise into two pieces and remove core. Slice each pineapple piece lengthwise into three strips. Arrange strips in a single layer over grill pan; cook 2-3 minutes on each side or until grill marks appear. Set aside. While pineapple cooks, chop onion and cut pepper in half lengthwise -- remove and discard seeds. Chop chile and cilantro. Combine onion, pepper, cilantro and salt in a small bowl. Zest the lime to measure 1 teaspoons zest and juice lime to measure 1 tablespoons juice. Add both to onion mixture; mix well.
Whisk taco seasoning mix and oil in a bowl. Add tilapia; turn to coat. Place two tilapia fillets on grill pan. Cook 2 minutes or until grill marks appear. Turn tilapia over; cook 2 minutes or until tilapia flakes easily with a fork. Remove tilapia from pan. Wipe out pan and repeat with remaining fillets.
As tilapia cooks, chop pineapple and add to onion mixture; mix well. Top tilapia with pineapple salsa.