1.Sprinkle The Beef Flank Steak With Steak Seasoning On Both Sides. Heat Olive Oil In A Skillet Over Medium Heat Until The Oil Shimmers, And Place The Flank Steak Into The Hot Oil. Quickly Brown The Steak On Both Sides, About 5 Minutes Per Side. Set The Beef Aside. 2.Stir Brown Sugar, Onion, Red Bell Pepper, Apple Cider Vinegar, Worcestershire Sauce, Tomato Sauce, And Tomato Paste Together In A Slow Cooker Until The Brown Sugar Dissolves. Place The Flank Steak Into The Slow Cooker, Immersing It In The Sauce. Set The Cooker On On High And Cook 4 Hours, Or Set On Low And Cook 8 Hours. 3.To Serve, Shred The Meat With 2 Forks, Or Remove The Meat, Chop, And Return To The Sauce. Toast Buns, And Serve The Sloppied Steak On The Toasted Buns.