Combine marinade ingredients together in a large, shallow dish. Add the chicken and coat evenly. Cover and marinate for 15 minutes if rushed, 1 hour if time allows, or over night, turning each chicken thigh occasionally in the marinade.
Preheat oven to 220°C | 430°F. Spray a baking pan / sheet with cooking oil spray, or lightly grease with oil. Arrange the chicken, potatoes and onion wedges on the baking tray / sheet. Drizzle the potatoes and onion with a small amount of olive oil and juice from half of the lemon. Season chicken. potatoes and onion with the extra salt and pepper to taste, and extra oregano. Toss the potatoes and onion through the oil mixture to evenly coat. Slice the remaining lemon into thick slices and arrange over the chicken.
Bake until the potatoes are golden/crispy on the outside and tender on the inside, and the chicken is completely cooked through (about 30 minutes). Change oven setting to grill / broil on a medium heat setting for about 5 minutes, or until crispy and golden brown. Serve with olives and feta cheese.
Notes
The longer the chicken is marinaded, the more flavour intense it will be when baking. Marinade adapted from this Greek Lemon Garlic Chicken Salad.