Preheat the oven to 400 degrees. Warm a large, heavy oven-proof skillet over medium heat. When the pan is warm add 2 tablespoons of olive oil and heat until it shimmers.
Meanwhile put the chicken thighs in a large bowl and season generously all over with salt and pepper. Add the remaining 2 tablespoons of oil and 2 tablespoons of harissa and using your hands or a large spoon toss the chicken with the sauce and oil until every piece is coated. Set aside for a few minutes while you do the rest of the prep.
When the oil is hot, add the onions and a nice pinch of salt. Sauce the onions until they are soft and beginning to turn translucent, stirring occasionally for about five minutes. Add the garlic and saute for just 30 seconds to a minute, just until the garlic is fragrant. Add the cumin and coriander and stir into the onions and garlic for about 30 seconds. The add the remaining harissa and stir all of that to coat the onion mixture.
If the pan looks dry, add another glug of olive oil then add the rice and stir. Once the rice is thoroughly coated with the oil and spices allow it to gently toast, stirring a bit, for about 4 or 5 minutes. Stir in the dates and olives.
With a vegetable peeler, peel just the orange part of the skin of the orange into strips about an inch wide and drop them right into the mixture. Cut the orange in half and squeeze in the juice. Add another 1/2 teaspoon of salt. Stir it all to combine again and then nestle the chicken pieces in a single layer on top of the rice. Scrape any leftover harissa from the chicken bowl into the pan too. Now, working around the pieces of chicken so as not to rinse off the harissa marinade, add the water to the pan evenly all around.
Put the pan in the oven uncovered and roast for 40 minutes. About 15 minutes before the time is up, open the oven and push any rice that isn't under the chicken or the liquid underneath, so that it cooks.
After the full 40 minutes the chicken pieces should be nicely golden brown and cooked through. Pull the pan out of the oven and cover with foil or a pan lid and let rest for about 5 to 10 minutes. Sprinkle the chopped pistachios over all and serve warm.