Place the ribs in a large saucepan and cover with cold water. Bring to a boil, reduce the heat and simmer gently for about 1 hour. Drain and let cool.
In a bowl, combine the cornstarch and water. Set aside.
In a small saucepan, combine the soy sauce, brown sugar, lemon and lime zest, harissa and cinammon. Bring to a boil, reduce the heat and simmer, stirring frequently, until syrupy, about 5 minutes. Add the cornstarch mixture and bring to a boil while whisking. Let cool.
In a large baking dish, toss the ribs with the sauce to coat well. Cover and refrigerate for about 12 hours.
Preheat the grill, setting the burners to high.
Grill the ribs for 5 or 6 minutes a side, brushing generously with sauce when almost done.
Place the ribs on a serving platter and sprinkle with cashews. Garnish with orange wedges.