In a bowl, mix marjoram, salt, pepper, and olive oil. Rub on pork.
Place pork in pressure cooker. Add lemon juice and water.
Close and lock lid, set pressure cooker to "meat/stew", adjust time to 25 minutes, and press "start/stop".
When done, natural release for 10 minutes, then do a quick release to make sure all pressure is released before opening lid. Carefully open lid. Using a slotted spoon, remove pork to a flat surface. Slice or shred pork.
Serve pork on warm tortillas with diced tomatoes, shredded lettuce, tzatziki sauce, and lime juice.