1.Pound pork using a meat mallet. Finely grate the rind from the lemon; squeeze juice. Combine pork, rind, half the juice, rigani, paprika, oil, salt and garlic in a medium bowl; toss well. Cover, refrigerate for up to 1 hour.
2.Meanwhile, halve cucumber lengthways; remove seeds. Grate cucumber coarsely; squeeze out excess liquid. Combine cucumber, mayonnaise, yogurt, mint, garlic and reserved lemon juice in a small bowl; mix well. Season to taste.
3.Cook pork on heated barbecue or grill pan over medium-high heat for 3 minutes each side or until browned and tender. Transfer to a plate; cover to keep warm. Heat buns on barbecue or grill pan for about 30 seconds each side or until just warmed.
4.To assemble burgers, place lettuce on the bottom half of each bun, top with pork, Tzatziki Mayonnaise and onion. Sprinkle with black pepper and fresh oregano or mint, if desired.
Rigani is dried Greek oregano with a distinct flavour, available from some delis. If unavailable, you can use dried oregano or ¼ cup chopped fresh oregano. Serve sandwiches with oven-roasted chips, sprinkled with crumbled fetta, if desired.Note