Combine 2 cans of condensed mushroom soup, 1 package dry onion soup mix, 1 1/4 cup water and 5 1/5 pounds of pot roast in a Crock-Pot. Set the Crock-Pot to high and cook for 3 to 4 hours or cook on low for 8 to 9 hours.
Another recipe, as found on Food.com, requires 6 peeled and cut potatoes, 5 peeled and cut carrots, 1 quartered onion, 2 to 3 pounds of boneless chuck roast, one-half cup of water or beef broth, 1 tablespoon of chives, 2 tablespoons of parsley, 1/8 teaspoon pepper, 1 package onion soup mix, 2 tablespoons Worcestershire sauce and 1 can of cream of mushroom soup.
Start by placing the carrots, potatoes and onion in the bottom of the Crock-Pot and top with the roast fat side up. Pour the water or beef broth into the Crock-Pot. Add the chives, parsley, pepper and onion soup mix, as well as the Worcestershire sauce and mushroom soup. Set the Crock-Pot to low, and cook the roast for 8 to 10 hours. Food.com notes that if the roast is frozen, it's possible to cook the roast using the low setting on the Crock-Pot overnight and add the other ingredients in the morning.