Heat a grill pan over medium-high heat for 5 minutes. As pan heats, peel pineapple half; cut lengthwise into two pieces and remove core. Slice each pineapple piece lengthwise into 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, removing and discarding seeds. Chop chile and cilantro. Combine onion, pepper, cilantro and salt in a small bowl. Zest the lime to measure 1 tsp. zest and juice lime to measure 1 tbsp. juice. Add both to onion mixture and 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.