Cut beef into 4-5-inch cubes and place in a mixing bowl. Add adobo to coat the meat, then add tomatoes, onions, sugar, and let it marinate for 3 hours. For best results, marinate overnight.
In a stock pot, add water and place beef on medium-low heat. Let it cook for 3 ½ hours, stirring every 20-30 minutes, and add salt to taste.
Once tender, shred the meat. Spoon the meat onto warm tortillas and top with cilantro, onions, and your choice of salsa.
