Preheat the oven to 375 degrees F. Put the garlic bulbs in a small tin and roast them until they are soft when squeezed, about 30 minutes. Remove them from the oven and let cool.
When the garlic bulbs are cool, slice the tops off and squeeze out the roasted garlic. Add the garlic to a food processor or a bowl, along with the lemon zest, lemon juice, thyme, cumin, crushed red pepper and salt, to taste. Add a little olive oil and puree or mash into a loose paste. Massage the mixture all over the chicken pieces and let sit for at least 1 hour.
Bring a pot of well salted water to a boil, over medium heat. Add the couscous and cook it until it's about 2/3 of the way cooked, about 5 to 6 minutes. Drain and reserve.
Coat a large saute pan with olive oil over medium-high heat. Add the chicken to the pan and brown it on all sides. Remove it to a plate, drain the fat and add the onions and celery. Season with salt, to taste, and the crushed red pepper. Deglaze with white wine, scraping up all the crud on the bottom of the pan and cook the onions and celery for 7 to 8 minutes. Stir in the tomato paste and cook for another 2 minutes. Add in the saffron, zucchini, cooked couscous, and chicken stock. Stir to combine, then taste and adjust seasoning, if needed. Transfer the mix to an ovenproof dish. Nestle the chicken, skin side up, in the couscous and cover with foil. Add some more chicken stock to keep everything nice and moist. Sprinkle with pine nuts and cover with foil. Place the baking dish on a sheet pan.
Roast the chicken for 20 minutes, covered, then remove the foil and roast for another 10 to 15 minutes.
Remove the chicken from the oven and top with scallions before serving.