In a 4- or 6-quart pressure cooker heat 1 tablespoon of the oil over medium heat. Cook meat until brown on all sides. Add more oil, if needed. Remove the meat and set aside. Drain off fat.
Place the rack in the pressure cooker. Return the meat to cooker and add the sweet pepper, onion, garlic, chipotle or jalapeno peppers, chili powder, and beef broth.
Lock lid in place. Place pressure regulator on vent pipe (if you have a first-generation cooker). Over high heat, bring cooker up to pressure. Reduce heat just enough to maintain pressure and pressure regulator rocks gently; cook for 35 minutes.
Allow pressure to come down naturally. Carefully remove lid. Meanwhile, heat tortillas according to package directions.
Transfer meat to a cutting board. Using the tines of two forks, pull the meat across the grain to form shreds. With a slotted spoon remove the vegetables to a serving platter. Combine with meat.
On each tortilla spoon about 1/2 cup of the meat mixture. If desired, top with guacamole, sour cream, cheese, and lettuce. Roll up tortillas. Makes 8 main-dish servings (4 cups meat mixture).