How to Make It
In a small saucepan, bring the water to a boil and stir in the couscous. Cover the saucepan, remove from the heat and let stand until the water has been absorbed, about 5 minutes. Fluff the couscous with a fork and let cool.
In a large bowl, gently mix the ground chicken with the couscous, chopped mint, ground cumin, grated lemon zest, pine nuts and 2 teaspoons of salt. With lightly oiled hands, pat the chicken-couscous mixture into 6 burgers. Cover the burgers tightly with plastic wrap and refrigerate until chilled.
Meanwhile, in a medium bowl, coarsely mash the avocados with a fork. Stir in the lemon juice, jalapeño and shallot and season with salt.
Preheat the oven to 325°. In a very large, deep skillet, bring the stock to a boil with the harissa. Season the burgers with salt and pepper. Set the burgers in the skillet and simmer over moderately low heat until cooked through, about 4 minutes per side. Transfer the burgers to a rimmed baking sheet, cover with foil and keep warm in the oven. Boil the poaching liquid over high heat until reduced to 1/2 cup, about 6 minutes.
Set the pitas on plates. Top with the chicken burgers and spoon some of the reduced sauce over them. Garnish the burgers with the avocado mash and the mint leaves and serve.
Harissa is available at Middle Eastern markets and specialty shops.