Combine all the ingredients for the beef filling except for the ground sirloin in a small bowl and mix well.

Crumble the ground sirloin into a large skillet (preferably nonstick), using a spatula to break up the meat, and cook until browned. Remove from the heat and drain any excess grease. Add the spice mix and 3/4 to 1 cup of water to the pan and simmer on medium-low heat for 20 minutes, until most of the moisture has cooked away. Remove from the heat before the meat is completely dry.

If you like, you can refresh the taco shells in the oven at 350°F for 7 to 10 minutes. To assemble to tacos, fill the taco shells with the beef filling and plenty of fresh lettuce and pico de gallo.