Although freezing keeps food safe for an indefinite amount of time, eventually the flavor will be affected. If the food is obviously damaged (shriveled, with white or frosty spots) it should be discarded.

Sometimes, when you cook over the stove or oven on other appliances, there are a lot of chances for moisture to evaporate.

Another problem that can arise is the meal sticking together, such as rice, sauce, and pasta.

When you feel the food might be drying or thickening, add water or other water-rich ingredients such as sauces or fatty ingredients such as butter or oil. 

Before preheating your pre-made meals, ensure to take them out of the meal prep bags used to store food. Plate the food in an appropriate dish/container, then place it in the oven. 

Moreover, cover the food with the help of aluminum foil to keep the moisture and prevent the meat from drying out.