Tip: From Frozen Tender Roast Cover it and put in the oven on low (I put it on at 250 degrees F). I normally put my roast in the oven at 3:00 pm and cook it until supper time at 7:00 pm. When you cook it frozen at a low temp for at least 4 hours, the roast will be the tenderest. You can cut it with a fork!