Heat 1 tablespoon of oil over medium-high heat in pot of a pressure cooker (To buy a Fagor 6-quart pressure cooker, $125.95, visit fccatalog.com or call 800-678-5752). Brown steak 5 to 6 minutes, turning once. Remove to a plate.
Reduce heat to medium and add remaining tablespoon oil to pot. Stir in onion, peppers, chili powder, cumin, salt and pepper. Cook 3 minutes, stirring occasionally. Stir in garlic and oregano; cook 2 minutes more.
Return steak to pot with any drippings, and top with tomatoes and beef broth. Lock lid in place. Over high heat, bring up to pressure, about 7 minutes. Lower heat to maintain pressure; cook 35 minutes.
Quick-release pressure by setting under cool running water. Open lid away from you, letting any excess steam escape.
Remove steak to a cutting board and cut across grain into 2-inch strips. Return sauce in cooker to medium heat and simmer, uncovered, 15 minutes. Meanwhile, shred meat with 2 forks and return to pot. Serve shredded beef and sauce on corn tortillas. Top with lettuce, diced red onion and cheese, if desired.