I assume that you have swapped out the regular pita bread for a high fiber, low calorie version. Switched the regular sour cream in the cucumber sauce to yogurt or lite sour cream.
The meat is basically a meatloaf. You might want to experiment with the composition of the loaf by using some chicken or turkey mixed in with the lamb/beef. The plus side is that the lamb has such a strong flavor that the poultry added is not really noticeable. There are a lot of recipes out there for gyro meat. Good luck and keep us posted with the recipe and results of your experiments.