When tilapia comes out chewy, it's usually because it's been overcooked. Every oven is different so make sure to check on the tilapia regularly as it bakes and take the fish out once it becomes tender and flaky. You may also want to use an oven thermometer to make sure your oven isn't overheating. Many home ovens have inaccurate temperature gauges. Cooking the fish at too high of a temperature can make it tough and rubbery, which nobody wants!