Well it depends what it is and how big it is. Really it just need to be boiling hot.
Whenever I cook I do extra to freeze and I label it according to portion size, eg, bolognese sauce x 4. A casserole type meal, in other words meat and sauce, is very dense. For something like that I would bung it in the microwave for 10 minutes defrost overnight in the fridge and then heat in a pan, stirring, until it boils. Then simmer for a few minutes. What sort of meal did you have in mind?
Agree it's better to defrost and heat slowly on the stove but bunging in microwave from frozen also does the trick. I usually do until it bubbles or is scalding all the way through and we're still here!
Some foods like Mac cheese and risotto don't reheat so well from frozen in the microwave. They're still edible but dehydrate a bit so either defrost first or add a bit of extra liquid halfway through.
I'd put the oven on 200 and then heat for about twenty minutes for a pie or 10 mins for fishcakes. Then use a knife to check how hot the centre is, take it out when the tip of the knife is very hot to touch.
Say you have a 5x5 inch block of frozen,cooked Rice.Lid off,defrost in the Micro for about 6 minutes.Check to see if the Block is loose yet(in its container).If not, keep checking every 5 Minutes on "defrost" setting.When the Rice Block slides out easy,place into a Larger,glass or large,micro bowl.Fork the lump to loosen it up,add 5 Tablespoons of water,stir as best you can.Back it goes,until 80 per- cent defrosted.Now,fork it hard,break up as many pieces as you can.Micro on "High"... check every 3 minutes until just right.Now is the time to add extra Soy sauce or butter and salt.When you Micro on High...keep the Lid on.Keeping a chunk or cooked rice handy in the freezer can really help your recipes,as the Rice keeps for a long time.We keep a block of "Chicken broth rice,soy sauce Rice and buttered rice in the big freezer.