1. Place all the ingredients in a container with a tight-fitting lid. Shake well.
2. Add the salt and pepper to taste.
For the salad:
1. Preheat the oven to 350°F.
2. Spread the almonds on a baking sheet and roast in the oven until lightly browned, about 10 minutes.
3. Place the spinach in a bowl and toss with the vinaigrette.
4. Transfer the dressed spinach leaves to a serving plate. Arrange the grapefruit sections on top and sprinkle with the almonds.
To roast whole, slivered, chopped or sliced almonds: Spread in an ungreased baking pan. Place in a 350°F oven and bake 10 minutes or until golden brown and fragrant; stir once or twice to ensure even browning. Note that almonds will continue to roast slightly after removing from oven.