1. FOR THE SUGARED PISTACHIOS: Adjust oven rack to middle position and heat oven to 325 degrees. Toss pistachios with egg white in small bowl. Using slotted spoon, transfer nuts to 8-inch-square baking pan lined with parchment paper; discard excess egg white. Add sugar and stir until nuts are completely coated. Bake, stirring mixture every 5 to 10 minutes, until coating turns nutty brown, 25 to 30 minutes. Transfer nuts to plate in single layer to cool.
2. FOR THE SALAD: Whisk marmalade, lemon juice, oil, shallot, mint, 1/4 teaspoon salt, and 1/8 teaspoon pepper in large bowl. Add arugula and oranges; toss and adjust seasonings with salt and pepper. Divide salad among individual plates; top each with portion of feta and sugared pistachios. Serve immediately.