1. Put onion and garlic in the bowl with the ultrablade knife. Mix at speed 12 for 10 seconds. Scrape the sides and the bottom of bowl. Replace the ultrablade knife with the mixer blade.
2. Add ground beef to the bowl. Launch the P1 simmer program. Half way through program, break up any large clumps of beef and restart time.
3. Add water and taco seasoning. With stopper removed, set P1 simmer program at temperature 270°F for 7 minutes.
4. To serve, fill taco shells with about 2 Tbsp. of meat mixture, then top with cheese, lettuce, tomatoes and other favorite toppings.