Place the minced turkey in a large bowl. Add the oregano, smoked paprika, red onion relish and some salt and pepper. Mix well with your hands.
Divide the mixture into eight portions and roll each piece into a ball. Flatten each piece to make a patty. Press the centre of each patty with three fingers to make an indention, which will help keep its shape while its cooking. Put the burgers on a plate, cover loosely with cling film and rest in the fridge for at least 15 minutes.
Preheat the barbecue to a medium heat.
Combine the mayonnaise and barbeque sauce in a small bowl.
When the coals are lightly coated with ash and are a medium heat, oil the grill grates. Grill the burgers, covered of possible, for about 10 minutes, turning once.
Spread the barbecue mayo over the base of each bun. Add a few salad leaves, a slice of tomato, a patty and a little more mayo, then put another bun with salad leaves, sliced tomato and patty on top so that you get a double burger. Top with another dollop of mayo. Serve immediately.