Can you go ahead and roast a frozen chicken?

No.
If you put it in the oven in a frozen state, the inside will take forever to cook.
The outside will be burnt, and the inside raw.
Microwave it with the thawing mode.

Thank you @ragingloli but won’t the microwave cook it though and not in a good way?

hence ‘thawing mode’

It’s probably too late—either you cooked it or you are dead from food poisoning.

@ragingloli gave you the right answer. Let me expand on it.

When you’re cooking chicken (or beef, for that matter), you need the inside to get to be at least 160–180 degrees. Not the skin or the outside, but the deepest internal portion. Why? Because if you don’t cook it all the way through, you give a very comfortably warm location for all sorts of bacteria and nasty stuff to grow. 160 degrees inside is high enough to kill almost all bacteria.

SO now take your chicken with the frozen inside. The thawed exterior will cook just fine. But the inside might not get over 80–100 degrees – if that – depending on how long you bake it, the inside might not even thaw. So you’re just creating a vector for warming up raw meat and unleashing lots of potential bacteria to make you sick.

In the thawing mode of the microwave, I don’t think the power is as strong. Yesterday I thawed ground beef in the microwave and it only took a couple of minutes before it was soft. There was a lot of liquid leaking out of it. I’m not sure if it was just moisture or the meat dries out but I didn’t care because my meal came out good anyway.

For things like whole chickens/birds, it’s best to let it thaw in the sink, not the microwave. Run warm water over it for a while and let it soak in warm water, draining the sink sometimes and refilling with warm/hot water. Keep it in the bag when you do this.

But yeah, don’t cook it without thawing it.

I know this is way too late but here is the physics behind the thaw first answers – if you care.

As a first order approximation let’s say a chicken is basically water. That will make the math easy and the chemical data is readily available.

It takes 1 calorie of heat to raise the temperature of 1 gram of chicken (water) 1 degree C. You can easily weigh the chicken and multiply that by the temperature difference between your refrigerator and the recommended cooking temp. of 85C.
But that only works when you have thawed chicken (water). Why? Because it takes a lot of energy to melt ice – even if the temperature is right at freezing. In fact, it takes 79.8 (call it 80) calories to melt i gram of ice. Yep. 80 times! The energy it takes to melt 1 gram of ice is the same as the energy required to raise the temperature of 1 gram of water 80 C!
Since a stove generally cooks from the outside in the thawed part of the chicken will heat up much faster than the frozen part. Much faster!

The high heat of fusion of water is why ice can cool a drink so well. It is amazing stuff.

For future reference, in winter I would have put the chicken in the sink (in a sealed bag) covered with neutral temperature water to thaw.

I hate the microwave “thaw” function. It seems just as uneven as the every other function, where you get ultra-hot and cold spots. It’s fine for things like ground beef that you’re going to handle extensively, but on a bird there might be a spot frozen solid that you don’t know.

I would not cook a chicken that has not been completely thawed in a natural, even way, unless it was a slow roast in a crock-pot, roaster oven or brown-n-bag.

I keep a large aluminum plate in my kitchen for defrosting things. It fits over half my sink. I place the things to be defrosted on the plate and trickle water over the edge of the plate. The aluminum is a wonderful heat sink and thaws chickens very quickly. Nearly as quickly as immersing them in water.

Here are Three Methods for thawing a chicken.

Note: if you are using the sink method, you will notice that they say not to use hot water as this will promote bacteria growth.

With the microwave method, you kind of need to take the chicken apart, rather than keeping it whole.

The safest method is thawing it out in the fridge, but it might take up to 24 hours for it to thaw, but if you plan ahead, next time, this is probably your best bet.

Thanks all for your help. I ended up making something else, and after overnite on the benchtop it’s thawed. I think.

Never thaw something by just leaving it out on the counter. You’re asking for bacterial growth. Plan ahead and put it in your fridge.

@elbanditoroso 180 is overkill. I wouldn’t go much higher than 165 myself and if one were cooking beef (steak, not ground beef) I would only cook it to 145.

@El_Cadejo My kitchen is unheated so it’s as cold as a fridge. I would never do this in summer.