Combine 2 quarts water and lentils in large saucepan; bring to a boil over high heat. Reduce heat to low; cover and simmer 30 minutes or until lentils are tender, stirring occasionally. Drain lentils.
Combine cooked lentils, green onions, vinegar, parsley, oil, salt, thyme and pepper in large bowl; mix well. Cover and refrigerate 1 hour or until cool.
Serve on lettuce leaves, if desired. Top with toasted walnuts before serving.
Notes
*To toast walnuts, spread in single layer in heavy skillet. Cook over medium heat 1 to 2 minutes, stirring frequently, until lightly browned. Remove from skillet immediately. Cool before using.