Heat oil in a large skillet over medium-high heat. Add chicken and cook 5 minutes per side or until browned and no longer pink in the center. Remove chicken to a plate and set aside.
Heat the broth in the same skillet. Add onion, garlic, cilantro, ginger, lemon zest, cumin and turmeric and cook for 5 minutes or until the onion is tender but not browned. Stir in coconut milk, nuts, sugar, red pepper and shrimp. Return the chicken to the skillet, cover and simmer for 10 minutes or until the chicken is heated through.
Remove the chicken and shrimp to a plate and keep warm. DO NOT discard the sauce in the pan.
In a small bowl, combine the tamarind paste and water. Stir into the sauce in the skillet and gently boil until thickened and the mixture measures about 1 cup. Evenly divide the chicken and shrimp among 4 plates.