Cut the red spines out of the tilapia fillets. Dice remaining fish into 1/3″ cubes, taking care to chop in vertical motions so you don’t mush up the fish. Put fish in a non-reactive stainless steel or glass bowl. Add lemon and lime juice and stir. Set aside while you chop the remaining vegetables.
Add red pepper, cucumber, jalapeño pepper, garlic, cilantro, salt and pepper. Stir to combine, cover and let marinade for at least 15 minutes and up to 3 hours, depending on your preference.