saute, onion, chayote, garlic, curry powder in butter for 5 mintues. stir in flour. add chicken broth, lime juice, bay leaf, ginger, tomatoes, salt and pepper and bring to a roiling boil. reduce heat and simmer fro 20 minutes stirring occasionally. add shrimp, cover and cook about 8 minutes or until shrimp turns pink. discard bay leaf before serving.