Stir The Soup, Chili Powder And Cumin In A 4-Quart Slow Cooker. Add The Beef And Turn To Coat. Cover And Cook On Low For 6 To 7 Hours Or Until The Beef Is Fork-Tender. Remove The Beef From The Cooker To A Cutting Board And Let Stand For 10 Minutes. Using 2 Forks, Shred The Beef. Return The Beef To The Cooker. Stir The Cilantro In The Cooker. Spoon About 1/4 Cup Beef Mixture Into Each Taco Shell. Top Each With About 1 Tablespoon Cheese. Top With The Lettuce And The Sour Cream, If Desired.