Place the meat, onion, garlic, and pepper in a pressure cooker. Add enough water to cover the meat and add the spices and salt. Cover the pot and cook under pressure for 1 1/2 hours (in a regular pot, cooking will take about 3 hours).

Remove the meat from the pot and shred it with a fork. Serve it on warm tortillas with chopped onion, cilantro, a few drops of lime juice, and green or red taco sauce.