Cut pork crosswise into thin slices. Slice into strips of 5 x 1/2-inch. Combine olive oil, mustard, lemon juice, garlic and oregano. Pour over pork slices. Cover and refrigerate for 1-8 hours.

 

Meanwhile, in small bowl stir together yogurt, cucumber, garlic and dill. Cover and refrigerate.

 

Preheat oven to 450 degrees F. Drain marinade from pork slices and place pork in single layer in shallow pan. Roast until crisp, about 10 minutes. Open each pita half to form a pocket. Distribute pork among each half. Top each sandwich with some chilled yogurt mixture and sliced onions.