Preheat your oven to 200 degrees.
Place the onions, garlic, tomatoes, and potatoes into a large roasting tray and season generously with salt and pepper. Chuck everything roughly together and roast in the oven for 20 minutes. (Don't worry about adding any oil or cooking spray - the moisture from the tomatoes will keep everything moist and prevent any burning).
Meanwhile, place your chicken thighs on a chopping board and slash each one 3 times with a sharp knife. Be careful not to cut all the way through - your cuts only need to be about half a cm thick. Mix together the oregano, chilli, and paprika, cayenne pepper, and lemon juice and add a generous grind of black pepper. Evenly rub the seasoning mix over the chicken, and set aside.
Remove the vegetables from the oven, and add the chorizo to the roasting tray. Chuck together using tongs or a large spoon. Place the chicken thighs on top of the veggie and chorizo mix. Place back in the oven for a further 20 minutes.
Remove from the oven, and turn the oven up to 220 degrees. Carefully spoon out some of the juices from the bottom of the tray, and drizzle over the chicken. Distribute the pepper strips between the chicken and the veggies, and return to the oven for 15 minutes, or until everything is cooked. Ideally, you'll want to ensure that your chorizo is 'hidden' between your veggies as much as possible, to prevent it from drying out!
Serve and enjoy!