You can melt the butter for the glaze in the microwave and combine it with the lemon. I find it harder to get the lemon zest to smooth out doing it this way.
Feel free to season the fish with any of your favorite seasoning and spices.
Cod should be cooked to an internal temperature of 135-145 degrees. Use a meat thermometer and/or check for flakiness. Gently press the thickest part of the fish using a fork. If it flakes easily, it is done. The flesh of the fish should be opaque.
If the fish is dry and tastes rubbery it was overcooked. Follow the tips above to avoid overcooking the fish.