Whisk the lemon juice, vinegar, honey (or sugar) and salt in a small bowl until honey is dissolved. Gradually pour in the oil and whisk to combine.
Shave the beets into ribbons with spiral slicer, or into thin discs with a mandoline or sharp knife.
Put the beets in a salad bowl with the onion and greens. Drizzle with enough dressing to coat, about 2 tablespoons, and toss together. Sprinkle the goat cheese and pistachios over the salad. Serve with additional dressing on the side.
Any kind of beet will work for this recipe, if you're in the mood for beets or brought home a load from the market. Choose smaller ones as they'll be sweeter and milder-tasting when raw.