Preheat oven to 375° and line a baking sheet with parchment paper. Scrub the beets and pat them dry. Rub them with 1 tablespoon of the olive oil, and sprinkle with 1/2 teaspoon sea salt. Place them on the prepared baking sheet and bake for about an hour, or until they are tender when pierced with a knife. Set aside and allow to cool.
Once they've cooled, peel the beets (the skin should peel or rub off pretty easily) and then slice into cubes about ½” to 1”. (This might get messy, so don’t wear your nicest white shirt while doing it.)
Supreme the oranges by trimming the tops and bottoms off the oranges and then carving off the peels and white pith. Carefully slice the orange segments away from the membrane, cutting as close as possible so not to waste too much of the orange. Cut the slices into ½” to 1” pieces.
Add the orange juice, lime juice and vinegar to a large bowl and mix together. Slowly add the remaining olive oil to the bowl while whisking the mixture. Add beets to the bowl, toss to coat, and season with the remaining salt and pepper. Gently fold in the orange slices. Cover bowl and let sit for about an hour to allow the flavors to mingle.
When ready to serve, toss the arugula into a bowl along dressed beets and oranges. Top with the toasted pistachios, scallions and parsley.