Cook pierogies in boiling water until just thawed, about 3 minutes. Drain and set aside. Meanwhile in a large nonstick pot or Dutch oven, over medium high heat, heat oil. Add chicken pieces, onion and garlic. Stir constantly until chicken is lightly browned, about 3 to 5 minutes.
Add flour; stir about 1 minute or until lightly browned. Stir in remaining ingredients and bring to a boil, stirring constantly. Reduce heat and simmer about 10 minutes, stirring occasionally, or until soup is slightly thickened.
Stir in thawed pierogies. Continue cooking 2 or 3 minutes or till heated through.