Melt the butter in a medium saucepan over medium heat. Add the rice, onion, and green bell pepper. Cook, stirring, for 3 minutes. Add the broth and Tabasco; bring to a boil. Stir. Cover and reduce heat to low; simmer for 15 to 20 minutes, or until rice is tender.
Add the shrimp, mushrooms, parsley, and salt and pepper, to taste. Cook for 5 minutes longer or until the shrimp is pink.
Spoon the shrimp and rice into a serving dish and garnish with the green onion tops.