Heat a non-stick pan over medium heat. Once hot, crumble in the beef and brown well while breaking it up into smaller pieces until no longer pink. Stir in the taco seasoning until fully combined. Stir in the water and bring to a simmer until most of the water evaporates. Season with salt if needed.
Meanwhile, warm the taco shells as directed on the package.
Spoon the ground beef into the taco shells, top with cheese, and onion. Serve with sour cream. Garnish with cilantro.
Notes
Make your own Taco Seasoning - Mix all ingredients together in a bowl (use what you need in the recipe to taste, save the rest in a sealed container for future use)