Chicken releases moisture as it cooks, so in order to keep panko chicken breast crispy when baking, you will need to do a few things: 1. Use thin chicken breasts so they can cook quickly 2. Cook at a high heat to keep the panko bread crumbs crispy 3. Cook the chicken breasts spread apart on a pan so the moisture doesn't accumulate, or cook on top of a cooling rack to keep the chicken out of the moisture.