Preheat oven to 450 degrees. In 9-by-13-inch baking dish, toss beets and 1 tbsp. EVOO; season. Spread in dish and roast 10 minutes. Place salmon on beets and brush with 1/2 tbsp. EVOO; season. Cover baking dish with foil and roast until salmon is still slightly pink in center, 15 minutes. Meanwhile, in bowl, whisk remaining 3 tbsp. EVOO, shallots, zest, juice and tarragon; season. Divide salmon and beets among plates with salad greens and drizzle with tarragon sauce.
