Place the washed and dried chicken thighs in a resealable plastic bag. Peel thin strips from a lemon using a lemon zester and add them to the bag. Squeeze out the lemon juice and pour it into the bag. Add the oregano and salt. Seal the bag and toss the chicken thighs in the marinade.
Heat up some oil in a cast iron skillet and add the chicken thighs from the bag. Sear the chicken thighs on both sides and remove them from the skillet.
Wipe the skillet clean using kitchen paper, heat up a generous amount of olive oil, and fry the diced onion in it. Stir in the rice. Pour a few spoonfuls of chicken stock into the bag containing the rest of the marinade, and then pour it and the remaining chicken stock into the skillet. Add salt, pepper, and oregano to the rice and let it cook for a while.
Place the chicken thighs in the rice, adding several slices of lemon in between. Put the skillet in a convection oven set to 360°F for 30 minutes.