Melt butter in large skillet on medium-high heat. Add mushrooms and onion; cook and stir 3 minute or until mushrooms are tender.
Stir water and Rice Mix into skillet. Bring to boil. Reduce heat to low; cover and simmer 15 minutes. Stir in shrimp. Cover. Cook 10 minutes longer or until rice is tender and shrimp turn pink. Remove from heat. Let stand 5 minutes.