Bring rice mix, 2 1/3 cups water, and 1 tablespoon butter to a boil in a saucepan. Reduce heat to low, cover, and simmer 25 minutes or until rice is tender.
Melt remaining 4 tablespoons butter in a large nonstick skillet over medium heat; add onion, bell pepper, and mushrooms, and saute 8 minutes or until tender.
Stir in crabmeat and oysters, and cook 4 minutes. Stir in rice, soup, and remaining ingredients; cook, stirring occasionally, 5 to 10 minutes or until thoroughly heated.