Thinly slice beet green stems and finely chop leaves; keep stems and leaves separate. Heat 1 tablespoon oil in large skillet over medium heat. Add stems and cook, stirring occasionally, until tender, about 3 minutes. Add remaining 1 tablespoon oil and garlic and cook, stirring, until fragrant, about 15 seconds. Add greens, vinegar and water and cook, stirring occasionally, until greens are tender and liquid has evaporated, 4-5 minutes. Stir in salt and remove from heat.