Melt margarine in medium saucepan over medium-high heat. Add bell pepper, green onions and rice; cook 2 to 3 minutes or until vegetables are tender and rice begins to brown, stirring frequently.
Stir in thyme, broth and mushrooms. Bring to a boil. Reduce heat; cover and simmer 20 minutes or until liquid is absorbed. Let stand 5 minutes before serving.