For the best results I recommend starting with a thawed roast so that it cooks evenly through; however, you can slow cook a frozen roast. I recommend brushing a little oil on the roast and seasoning it liberally with whatever spice blend you want to use. You can skip searing it since it won't have the same results as a thawed roast does. Put the roast in the bottom of the slow cooker and add the thin liquid. The thinner the liquid, the faster the roast will thaw and begin to cook so I would skip any thickening agents like a roux or gravy packets. Use about 2 cups of thin liquid and slow cook on high for about 2 hours. Then you can add in the vegetables and any thickening agents you want to use and slow cook on high for another 6 hours or until the internal temperature of the roast is around 200℉/93℃