Place the chicken thighs on a board and season generously all over with salt and freshly ground black pepper.
Heat the oil and a small knob of butter in a large non-stick pan set over a medium heat. Lay the chicken thighs in the pan, skin-side down. Press something heavy on top (a meat press or pan filled with cans of beans is ideal) for extra crispiness. Cook for about 8 minutes, remove the weight, and flip them over. Continue to cook for another few minutes - or until they are cooked all the way through. Remove from the pan and set aside.
Add the lemon slices and oregano to the pan and reduce the heat to low-medium. Fry for about 5 minutes, stirring occasionally, or until the lemons start to soften and take on a nice colour. Take care not to burn them or they will become bitter. Discard the oregano and place the lemon onto a chopping board. Finely chop the lemon and tip into a bowl. Set aside.
Tip the orzo into the pan and cook for 1 minute, stirring constantly to coat in all the delicious buttery, herby, lemony oil in the pan.
Pour in the stock, stir well and bring to a simmer. Reduce the heat and continue to cook for 10 minutes, stirring occasionally. Orzo tends to stick to the bottom of the pan if left unattended, so keep checking and giving it a gentle stir to prevent this from happening. If it does stick to the bottom of the pan, give it a good scrape with a wooden spoon and it should loosen. If the orzo is looking too dry before it has finished cooking, add a splash more stock (or water).
Once the orzo has cooked, stir in the spinach, Boursin, reserved finely chopped caramelised lemon, half the grated Parmesan and a generous grind of black pepper. Add a squeeze of lemon juice, to taste, and continue to stir until the spinach has wilted and the Boursin has melted. Taste again and adjust the flavours, as necessary.
Scoop the lemon orzo into bowls. Chop the chicken into strips and arrange on top. Sprinkle with more grated Parmesan and a few fresh oregano leaves. Enjoy!