Position rack in upper third of oven; preheat broiler to high. Line a rimmed baking sheet with foil.
Toss chicken with 1 tablespoon oil, cumin, paprika, cayenne and ⅛ teaspoon salt. Spread evenly on the prepared pan. Broil until just cooked through, 5 to 7 minutes.
Meanwhile, mash garlic and the remaining ⅛ teaspoon salt into a paste with a fork. Transfer to a medium bowl and whisk in lemon juice and the remaining 2 tablespoons oil. Add the chicken and let stand for 5 minutes, stirring occasionally.
Divide hummus among 4 shallow bowls or plates. Top with the chicken and any remaining dressing, cucumber, tomatoes, onion and parsley.
