Place Beef In Slow Cooker, And Cover With Onion. In A Medium Bowl, Stir Together Ketchup, Worcestershire Sauce, Brown Sugar, Salt, Paprika, Mustard, And 1 Cup Water. Pour Mixture Over Beef And Onions. Cover, And Cook On Low For 9 To 10 Hours, Or Until Meat Is Tender. Mix 1/4 Cup Water With Flour To Form A Paste, And Stir Into Goulash. Cook On High For 10 To 15 Minutes, Or Until Sauce Thickens.