1. If frozen, thaw shrimp according to package directions. Devein, if desired, and set aside.
2. Cook onion and next 4 ingredients in hot oil in a 4-qt. cast iron Dutch oven over medium-high heat, stirring constantly, 10 minutes or until chicken is lightly browned. Stir in rice and next 5 ingredients.
3. Bake, covered, at 325° for 50 minutes. (Do not remove lid or stir.)
4. Remove from oven, and stir in shrimp. Bake, covered, 10 more minutes or just until shrimp turn pink. Garnish, if desired.