How to Make It
Preheat the oven to 425°. Finely grate the zest of 1 orange. Using a sharp knife, peel both oranges, removing all of the bitter white pith. Thinly slice the oranges crosswise; set aside. In a large bowl, toss the shrimp with 2 tablespoons of the olive oil, 1 tablespoon of the tarragon and the salt, pepper and garlic.
Heat a large ovenproof skillet. Add the shrimp in a single layer and cook over moderately high heat, stirring, for 1 minute. Remove the skillet from the heat.
Roast the shrimp in the oven for 2 minutes. Using tongs, turn the shrimp and add the orange juice and zest. Roast for another 1 to 2 minutes, or until the shrimp are opaque throughout.
Meanwhile, in a large bowl, whisk the vinegar into the remaining 2 tablespoons of oil. Whisk in the juices from the shrimp. Add the arugula and toss; transfer the salad to plates. Arrange the shrimp, oranges and onion on the salads, garnish with the remaining tarragon and serve.