Shrimp, Avocado, and Grapefruit Salad

A shrimp, avocado, and grapefruit salad, perfect for a weekday evening but elegant enough to serve to guests, will become a regular dinner dish.
Preheat a large skillet over medium-high heat. Add 1 1/2 teaspoons of oil to the skillet; stir to coat. Sprinkle the shrimp with 1/4 teaspoon salt and 1/8 teaspoon pepper. Add the prawns to the pan; cook for 3 minutes or until the prawns are tender, stirring frequently. Remove from the mold; keep warm.Peel the grapefruit and put it on a plate, leaving 3 tablespoons of juice. Combine the grapefruit juice, remaining 2 tablespoons of oil, remaining 1/4 teaspoon of salt, remaining 1/8 teaspoon of pepper, tarragon, brown sugar, and shallots in a large bowl, mixing well with a whisk. Add the lettuce leaves; toss to combine. Place 2 cups of the salad mixture on each of the 4 plates. Add 3 avocado slices to each serving; spread the shrimp and grapefruit evenly over the portions.