Grilled Shrimp, Pink Grapefruit, and Avocado Salad

Assemble the salad. Cut the peel from the grapefruit using a sharp knife. Cut out the segments, reserving the juice. Squeeze the juice from the remaining pith and pulp. Strain and measure 3 tablespoons juice. Set remaining juice aside for another use. Whisk the Dijon, remaining 1/4 teaspoon salt, remaining 1 teaspoon lime juice, and the reserved grapefruit juice together. Whisk in remaining 3 tablespoons olive oil. Line 2 salad plates with lettuce and arugula. Arrange the shrimp, grapefruit, and avocado on top of the greens. Drizzle with grapefruit vinaigrette. Serve immediately.