Cut beef into 3/4-inch wide strips; set aside. Heat oil in large nonstick skillet. Add onion and pepper; cook and stir 4 minutes or until crisp-tender over medium heat.
Stir in garlic, lime juice, cumin and oregano. Add beef; cook and stir 1 minute or until hot. Meanwhile, warm tortillas according to package directions.
Divide beef mixture and place down center of tortillas. Fold tortilla edges over beef and top with salsa and yogurt.