For the spice blend: Set a small skillet over medium-high heat. Add the cumin, coriander and chili flakes and toast, stirring constantly, until the aromas are released; be careful not to burn the spices or they will turn bitter. Pour the spices into a spice grinder, mortar or re-purposed coffee grinder and let cool for a couple of minutes. Add the smoked paprika, cinnamon, hot paprika and allspice and grind to a powder. The blend can be stored in an airtight glass jar for up to 3 months.
For the spiced butter: Combine the butter with 1/4 cup of the spice blend in a medium bowl. Beat with a wooden spoon until well combined. Simple, but oh so special.
For the chicken: To spatchcock a chicken, cut along each side of the backbone with sharp scissors or poultry shears. Remove the backbone, and reserve it for stock; I collect poultry bones in a bag in my freezer until I have enough for a big batch of stock. Turn the bird breast-side up and apply the weight of your body to the palm of your hand to flatten the bird. Sprinkle the skin and cavity of the bird generously with sea salt; slather the chicken with 6 tablespoons of the spiced butter. If possible, salt and season the bird 4 to 10 hours before you are ready to cook and let sit in the refrigerator. About 1 hour before you plan to grill, let the chicken come to room temperature.
Heat a grill to medium-high heat or set up for indirect heat. Bring a kettle of water to a boil.
Toss together the fava beans (pods and all!), spring onions, green garlic, 1 tablespoon olive oil, the juice of 1/2 lemon and a good pinch of salt.
Place the couscous in a large bowl and season with some salt, 2 tablespoons olive oil and the lemon zest. Pour the boiling water over the couscous to cover; let sit, covered, for 25 to 30 minutes.
Meanwhile, grill chicken breast-side down, covered with vent open, until nicely charred, 10 to 15 minutes. Flip and cook 15 to 20 minutes more. Let the chicken rest for 15 minutes before carving.
While the chicken is resting, grill the spring onions until nicely charred, turning once, 8 to 10 minutes. Grill the fava beans until the pods begin to open, 1 to 2 minutes per side. Remove the vegetables from the grill and return them to the vinaigrette; give them a toss and taste for seasoning.
Before carving the chicken, slather on the remaining 2 tablespoons of spiced butter and top with the remaining lemon juice. Serve with the couscous and vegetables with vinaigrette.
Spatchcocking a chicken facilitates fast and even cooking - essential when cooking over an open campfire, because it enables you to cook the meat evenly.