When baking pans get covered in stuck-on stains, you can easily clean them away with hot water, dish soap, and a little elbow grease.
Let the tray soak overnight. This will help to loosen all the gunk, making it easier to scrub the burnt-on juices away with a sponge or dish brush.
Once you're done scrubbing, just rinse and dry it off, and it's ready to go back in the oven for more roasting at any time.
If you still see some stains, you can make an effective cleaning paste using baking soda and hot water, which you'll want to spread all over the inside of the tray.
Let the mixture sit for about half an hour, then scrub away the grease stains before rinsing the paste away.