In a bowl, combine the oil, lemon juice, garlic, lemon zest, chili powder and pepper. Place half in a resealable plastic bag; cover and refrigerate remaining marinade. Add meat to bag. Seal and turn to coat; refrigerate for 4-8 hours.
Drain and discard marinade. In a skillet, heat reserved marinade. Add meat and green onions. Cook and stir until meat reaches desired doneness. Using a slotted spoon, place about 1/2 cup meat mixture down the center of each tortilla. Top with salsa if desired. Fold sides over meat mixture.