In large bowl, combine 2 Tbsp olive oil, garlic, lemon zest, ras el hanout, and salt. Add chicken and onions and toss to coat evenly. Spread in single layer on sheet pan. Bake in preheated oven until chicken is cooked through to an internal temperature of 165 F and onions are slightly caramelized, about 20 minutes. Remove from oven and allow chicken to cool before slicing into thin strips.