In a bowl whisk together 2 tbsp olive oil, salt, pepper, lemon juice and zest, oregano, thyme and garlic.
Heat 1 tbsp olive oil in a cast iron skillet on medium high heat. Once the oil is hot, place the thighs skin side down in the skillet and sear for approximately 5 minutes until golden in colour. Remove the chicken from the skillet and set aside.
Preheat the oven to 200 degrees Celsius (400 degrees Fahrenheit)
Place the fennel and onion wedges in the skillet and then top with the chicken thighs and lemon slices. Pour the lemon and herb sauce over top and then place the skillet in the oven to bake for 25 minutes. Half way through cooking spoon some of the liquid from the bottom of the skillet over the chicken and then return to the oven to continue cooking.
Once the chicken is cooked through and the fennel is tender, turn the oven to broil and move the skillet to the top rack to crisp up the skin for 2 to 3 minutes. Keep a close eye on it to make sure it doesn't burn.
Remove from the oven and sprinkle with lemon zest before serving