In large bowl, combine beef, bell peppers and onion. In small bowl, combine chili powder, lime peel, garlic, salt, cumin, oil and lime juice; blend well. Pour lime mixture over beef mixture; cover and refrigerate 1 hour to marinate.
Heat 12-inch nonstick skillet over medium-high heat until hot. Add beef mixture; cook and stir 6 to 8 minutes or until beef is browned.
Spoon about 1/2 cup beef mixture onto half of each warm tortilla. Fold tortilla over filling. If desired, serve with chopped tomatoes, lettuce, salsa, sour cream and guacamole.