In a non-stick pan over medium heat, brown the beef, using a spatula to break it up into smaller pieces. Once the beef is partially browned, add the taco seasoning and a 1/4 cup of water and bring to a simmer until most of the water evaporates. Then stir in half of the cheese. Remove from heat.
Meanwhile, warm the taco shells as directed on the package.
Spoon the ground beef into the taco shells, top with lettuce, tomatoes and remaining cheese. Serve with sour cream.
Notes
Make your own Taco Seasoning - Mix all ingredients together in a bowl