In a blender, combine the olive oil, lemon juice, onion, and garlic. Blend until smooth.
Pour the mixture into a large bowl and add the salt, pepper, oregano, paprika, and Greek yogurt. Stir until fully combined.
Dip the the chicken thighs to the bowl, ensuring each piece is well coated.
Transfer the coated chicken to a baking dish to marinate (approx. 34 cm x 23 cm). Pour any remaining marinade over the chicken.
Cover and refrigerate for a few hours or overnight for the best flavours and tenderness. (See notes for shorter marination time)
Remove the chicken from the fridge and let it sit at room temperature for about 30 minutes before cooking.
Preheat the oven to 180°C (356°F) (fan-forced).
Bake uncovered for 60 minutes, or until golden and cooked through. (See notes below for browning and temperature tips.)
Remove from the oven and let the chicken rest for 10 minutes before serving.