Arrange the thigh pieces in a large baking tray. Put half of the oil in a large frypan over a medium high heat and fry the potatoes until golden brown (add more oil if you need), then put them in the pan with the chicken.
Combine the vinegar, lemon juice, garlic, oregano, parsley, onion, salt and pepper with the rest of the oil and pour this mixture over the chicken and potatoes.
Bake in the preheated oven for 75 minutes, basting the chicken and potatoes with the sauce mixture. Let rest for 5 minutes and serve hot.