Rinse the Swiss chard and beet greens, set aside. Cut the stem of the Swiss chard from the leaves and dice up. Cut the chard and beet leaves into 2" slices. Slice the onion into half-moons and dice the beet.
Heat a large sauté pan over medium heat. Add olive oil and allow to heat thoroughly. Add diced beets, chard stems and onions, sauté until onion is soft and translucent, about 10 minutes.
Stir in the garlic, Swiss chard and beet greens, toss well. Allow the greens to wilt and become vibrant. Add a small amount of water if necessary to help the greens wilt.
Season with salt and pepper to taste. Serve immediately.