Cut pork loin filet in half lengthwise and thinly slice.
In large skillet over medium-high heat, heat 1 tablespoon oil. Stir-fry half the fresh pork loin filet 7-8 minutes until browned; set aside. Repeat with remaining oil and pork slices.
Layer warm pitas with shredded lettuce, pork slices, tomatoes and feta. Top with tzatziki sauce.