1) In a medium glass bowl, combine the spice mixture, 2 tablespoons of olive oil, the lemon zest, lemon juice and harissa. Add the chicken thighs and stir to coat. Cover the bowl with clingfilm and refrigerate at least 1 hour or up to 3 hours.
2) Warm the chicken stock and add the saffron strands, then allow to steep at least 1 hour or up to 3 hours.
3) Preheat the oven to 180C/Gas 4.
4) Remove the chicken thighs from the marinade. In a casserole dish over high heat, brown the chicken thighs on both sides in 2 tablespoons of olive oil, about 2-3 minutes per side. Set chicken aside on a plate.
5) Reduce the heat to medium, add 1 tablespoon of olive oil to the pan and saute the onion until golden, about 5 minutes. Place the chicken thighs on top of the onions and add any accumulated juices from the plate.
6) Arrange the courgettes, yellow squash and tomato quarters on top of the chicken and tuck in the prunes and olives. Season well with salt and pepper. Pour over the chicken stock and saffron. Cover and place on the bottom rack of the oven.
7) Let cook undisturbed for 1 1/2-2 hours, until the vegetables are tender and the chicken is falling off the bone. Remove from the oven and transfer the contents of the casserole dish to a large serving dish.
8) Heat 2 tablespoons of olive oil in a small saucepan over high heat until hot but not smoking. Add the almonds and fry until the skins begin to crackle, about 2-3 minutes. Pour the almonds and hot oil over the vegetables and chicken on the serving dish.
Sprinkle with the chopped parsley and serve, spooning over the sauce in the dish. Garnish each plate with the lemon quarters.
Combine the spices in a coffee grinder and grind to a medium-fine powder. Add the salt and pepper. Store in an airtight container, if not using immediately.
Cook's Note: If you're using a tagine, an unseasoned ceramic tagine may crack in the oven. Before using the tagine for the first time, submerge and soak it overnight in cool water. Pat dry and rub the inside with 1 tablespoon of olive oil, then place in 180C/Gas 4 oven for 1 hour. Allow to cool, then proceed with the recipe.