For the garlic chicken: Preheat the oven to 350 degrees F. Put the garlic bulbs straight on the oven rack and roast them until they are soft when squeezed, about 30 minutes. Remove them from the oven and let cool. Turn the oven up to 375 degrees F.
While garlic is roasting, prep the chicken. Into a food processor or a bowl, add the lemon zest and juice and set aside. When the garlic bulbs are cool, slice the tops off and squeeze out the roasted garlic into the bowl or food processor along with the 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.
For the couscous: Bring a pot of well salted water to a boil over medium heat. Add the couscous and cook it until it's about two-thirds of the way cooked, 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 celery and onions. Season with salt and crushed red pepper. Deglaze with the white wine, scraping up all the crud on the bottom of the pan, and cook 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, and 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, and then remove the foil and roast for another 10 to 15 minutes. Remove the chicken from the oven and top with scallions before serving.