In A Large, Heavy Pot, Heat Olive Oil On Medium Heat. Add The Onions And Cook Until Translucent, About 5 Minutes. Add The Tomatoes, Roughly Chopping Them In The Pot. Add The Barbecue Sauce, Increase Heat To Medium High And Simmer For 10 Minutes. Add The Chuck Roast. Bring To A Low Simmer, Cover And Slow Cook Until Meat Is Very Tender, Stirring Occasionally, About 3 Hours. Remove The Meat From The Pot. Use A Fork And Knife To Separate The Roast Into Small Pieces. Set Aside. 3 Increase The Heat On The Pot To Medium/Medium-High, Uncover, And Reduce The Liquid Until Thick. Stir Often To Prevent Burning. 4 Return The Meat To The Liquid In The Pan. Warm Both Thoroughly. Add Salt And Pepper To Taste. Serve On Buns. Makes Approximately 12 Sandwiches.