Place the first 5 ingredients in a small bowl and whisk to combine. Divide and mound the spinach on 2 plates. Top with the shrimp and grapefruit. Drizzle with the dressing, sprinkle with almonds, and serve.
Note: To segment the grapefruit, first carefully cut off the peel and pith. Use a paring knife to cut the grapefruit segments out of their surrounding membrane. Squeeze the remains of the grapefruit after segmenting to get the juice required in this recipe.
Note: To toast the almonds, place in a single layer in a small baking pan. Bake in the oven at 300 degrees F for 10 to 15 minutes, or until lightly toasted.