Place a frying pan over a medium heat, and fry the onions and sage in half of the olive oil for 10 minutes until golden and soft.
Add the onion and sage mix to a bowl with all the other ingredients. Mix gently, and shape into 4 patties, about 1.5 cm thick.
Fry the patties in the remaining olive oil for around 5 minutes on each side or until fully cooked through.
Notes
It's important that turkey is properly cooked through. If you pierce the burger with a sharp knife or fork, any juices that run out should be clear in colour.