Trim The Roast Of Any Excess Fat, And Season With Salt And Pepper. Heat Olive Oil In A Large Skillet Over Medium-High Heat. Place The Beef In The Hot Skillet, And Brown It Quickly On All Sides. Transfer The Roast To A Slow Cooker And Top It With The Chopped Onion. Season With Chile Peppers, Chili Powder, Cayenne Pepper, Hot Pepper Sauce, And Garlic Powder. Add Enough Water To Cover 1/3 Of The Roast. Cover, And Cook On High For 6 Hours, Checking To Make Sure There Is Always At Least A Small Amount Of Liquid In The Bottom Of The Cooker. Reduce Heat To Low, And Continue Cooking For 2 To 4 Hours, Or Until Meat Is Totally Tender And Falls Apart. Transfer The Roast To A Bowl And Shred It Using Two Forks (Reserve 2 Cups Of Cooking Liquid, If Desired). Serve In Tacos Or Burritos (See Cook'S Note).