Overcook them. Most of the world is trying to get their fish to the point of slight moisture, just before it is flaky, and, therefore, overdone.

Granted, there is a pretty fine line between undercooked and overcooked fish, and often, it just takes some experience to know the difference. But you can always use the blade of a knife to pry up a piece of fish (preferably at the thickest part) to see if it's too wet, just done, or beginning to flake - and therefore whether it needs a little more cooking or not.

If, in your case, the outside of the fish is constantly getting done while the inside is still not cooked, you may have to use a lower temperature for slightly more time, to allow the heat to reach the center of the fish before the outside is overdone.