Mix tomato paste with 1 cup sour cream; 1/4 cup dressing; and 1-1/2 tsp. each garlic powder, coriander and cumin until blended. Pour over chicken in shallow dish; turn to evenly coat both sides of each thigh with sour cream mixture. Refrigerate 3 hours to marinate.
Heat oven to 400°F. Cover rimmed baking sheet with foil; spray with cooking spray. Place 2 large skewers, parallel to each other and 1-1/2 inches apart, on prepared baking sheet. Repeat with 2 additional skewers.
Remove chicken from marinade; discard marinade. Fold chicken thighs in half, then thread evenly onto skewers, tightly threading half the thighs onto each set of parallel skewers.
Drizzle with 2 Tbsp. of the remaining dressing.
Bake 30 to 35 min. or until chicken is done (165°F). Remove chicken from oven. Heat broiler.
Broil chicken, 4 inches from heat, 5 min. on each side or until golden brown on both sides. Meanwhile, mix remaining sour cream, dressing and seasonings until blended. Reserve for later use.
Stand 1 kebab on work surface, then use sharp knife to cut chicken vertically, from top to bottom, into thin strips.
Stack pita breads on microwaveable plate; cover with damp paper towel. Microwave on HIGH 30 sec.
Spread pita breads with hummus; top with lettuce, tomatoes, cheese and chicken. Drizzle with reserved sour cream mixture; roll up.