Steam cook the green beans until just tender, then rinse in cold water so they stay green.
In a pan on medium heat, toast the filberts just until golden.
Sprinkle the mushrooms with the lemon juice.
Prepare a vinaigrette with the salad oil, vinegar, mustard and salt and pepper.
Arrange the mesclun on four salad plates and attractively place the green beans, mushrooms, and mango slices on top. Pour the vinaigrette evenly over the salads then top with the foie gras and sprinkle with the toasted nuts.
Makes 4 servings.