In a microwave-safe baking dish or casserole, combine green beans and water. Cover and microcook on 100 percent power (high) for 12 to 14 minutes or until just tender, stirring once after 6 minutes. Drain off water. Cover; keep warm.
In another baking dish, microcook walnuts in butter or margarine on high for 1-1/2 to 2-1/2 minutes or until butter is bubbly and just beginning to brown, stirring after 1 minute.
Add walnut mixture and cheese to beans in casserole; toss to combine. Serve warm. Makes 4 side-dish servings.