Brown ground beef in skillet.
Add taco seasoning packet to meat and mix well, omitting any water called for on the packet.
Add tomato soup, and diced tomatoes with green chilis.
Place 1/4 cup of water into tomato soup can and swirl it around to remove all of the tomato soup.
Pour water from tomato soup can into meat mixture.
Stir well until everything is mixed together.
Bring Mixture to a boil.
Add sour cream to pan and mix well.
Add tortilla pieces to pot and mix well to thoroughly incorporate.
Bring mixture to a boil again.
Reduce heat to a gentle simmer.
Top with cheese, and cover pan with a lid.
Allow cheese to melt in covered pan over very low heat. (About 5 to 10 minutes)
Remove pan from heat and allow to rest for 10 minutes before serving. (This allows mixture to thicken, so it's not a runny mess.)