Heat the olive oil in a medium-sized frying pan over a medium heat. Add the sliced onion and fry for 10 minutes, or until softened and turning golden brown. Add the sugar, garlic, cumin, oregano and chilli and cook for a further 3 minutes. Stir through the shredded turkey and cook for a further 10 minutes or until everything is gently warmed. Season to taste.
In small bowl, combine the chopped red onion, lime zest and juice, half the coriander and the tomato. Season to taste.
Take a tortilla and fold it in half. Generously fill with the warm turkey mixture and top with the onion and lime topping and jalapeños. Serve with the wedges of lime and sour cream.