Season all sides of the beef with a fair amount of salt and pepper. Flour both sides of the chuck roast. In a large Dutch oven, skillet, or if your crock pot has a stove top insert, heat 2 tablespoons of oil over moderately high heat. Add the pot roast and brown. Get a nice brown crust on each side of the beef.
Place the beef in the crockpot. Sprinkle the garlic and onion over the beef.
Add the crushed tomatoes, water and add spices.
Cook in crock pot on low for 6 - 8 hours. Let meat cool in the liquid. Shred meat and set aside.
Warm corn tortillas by dampening a clean kitchen towel with water. Place the corn tortillas on the wet towel and fold the towel over the tortillas. Place the package in a gallon zip lock bag, but do not seal.
Place them in the microwave and cook for two minutes at 50% power. Let them steam in the bag for 4 minutes before removing.
Toppings for tacos: Shredded Cabbage, Avocado, guacamole, Sour Cream, sliced radishes, cilantro, salsa.