Heat butter in a medium-size saucepan over medium heat. Add garlic, celery, carrots and mushrooms; cook 5 minutes.
Add rice pilaf mix with seasoning packet, water and pepper. Bring to a boil. Reduce heat and simmer, covered, for 17 to 22 minutes, until rice is tender. Add white beans. Garnish with sliced green onions. Makes 4 servings.