Let the meat marinate for at least 6 hours. Transfer beef and liquid to crockpot. Add just enough water to reach the halfway mark on your roast. Cook for 6 hours on a medium/high setting. Halfway through the six hours, stir the tomato paste into the liquid and add the pearl onions. When meat and onions are cooked, remove roast from crockpot and trim away the cooked fat, break the meat into small chunks. Pour the remaining liquid and cooked onions, with the chunked meat, into a large baking dish. Cook on 400 degrees for 90 minutes, until liquid has reduced and the onions have carmelized.
Enjoy over plain rice or mashed potatoes.