Sweet and Sour Chicken

3 tablespoons flour
1/2 teaspoon garlic powder
1/2 teaspoon salt
1/2 teaspoon pepper
1 1/2 pounds chicken, cubed
3 tablespoons oil, divided
3 ribs celery, sliced
2 medium green peppers, diced
1 medium onion, diced
1/2 cup ketchup
1/2 cup lemon juice
1 cup crushed pineapple with syrup
1/3 cup packed brown sugar

In a shallow dish, combine the flour, garlic powder, salt and pepper.  Coat cubed chicken, saute in 2 tablespoons oil over medium-high heat for 8-10 minutes or until tender.  Remove chicken and saute celery, green pepper and onion in remaining for 5 minutes or until crisp tender.  Return chicken to pan.  Combine ketchup, lemon juice, pineapple and brown sugar, add to skillet.  Bring to a boil; cook and stir for 1-2 minutes or until heated through.