Lucky I know in the past you have said that you cook mostly by microwaving, so now I am wondering if, you are having this problem in the microwave oven or, is it also when using your conventional oven that this occurs too, ?
The reason I ask, is that like Faye, I have not come across any problem, but then, I would not normally use my microwave for cooking this sort of meal so perhaps therein lies the difference ? To be truthful, my microwave is not used an awful lot for producing main meals at all really. Sauces, custards, instant porrige, scrambled eggs heating and thawing and that is about it really. Many would say it is under utilized but I have never really enjoyed main meal meat or chicken dishes cooked that way. I use either a slow cooker, or the conventional oven, and like Faye I also usually saute the onions first before putting them into the casserole dish with the meat which I always sear beforehand too. I believe that it not only seals in the flavour of the meat, but it also renders the onion more easily digestable .
Of course there are times when I do cook them from raw, but that would be in recipes where they are chopped very finely, such as in meat balls .
If this is happening in the conventional oven, I wonder if the thermastat is cooking to the true temperature ? If you do not use your conventional over for baked goods such as cakes or slices, you may not notice that it is not cooking true to a set temperature.
But then of course, you would also notice that meat such as blade steak was not as tender as it should be either.
In that case it is a mystery to me why you would be having such a problem.