1 large onion, sliced into rings
1 (3- to 4-pound) sirloin beef roast
1/2 cup water
2 (1.25-ounce) packages taco seasoning mix, divided
16 (6-inch) flour tortillas
4 cups (16 ounces) shredded Cheddar or Monterey Jack cheese
Toppings: diced tomatoes, diced onions, sliced jalapeno peppers, sour cream, black beans


Place onion in bottom of a 5-quart slow cooker; add roast and 1/2 cup water. Sprinkle 1 package taco seasoning mix over top of roast.
Cover and cook on high 5 hours. Remove roast, and shred with two forks; return to slow cooker, and stir in remaining package of taco seasoning mix. Cover and cook on high for 30 more minutes or until boiling.
Heat tortillas according to package directions. Using a slotted spoon, spoon beef mixture evenly down center of each tortilla; top with cheese and desired toppings, and roll up. Serve with Pico de Gallo.