Heat a large skillet over medium heat. Add the ground beef and onion and cook until browned, stirring occasionally breaking up any large pieces.
Once browned, drain off any extra grease. Then add in the taco seasoning, salsa and water. Bring to a light simmer. Add more water as desired.
Serve in taco shells as-is or place in a 9x13 dish to bake. Then add cheese and bake at 400°F for 10 minutes.
Add desired toppings.
Optional: You can also add 1-2 Tablespoons of refried beans to the base of the beef tacos. If I'm adding them, I like to place them in a zip top bag and then snip the top off and place it on the bottom of the shell.