Separate leaves from stems. Cut stems into pieces on a diagonal. Cut leaves into bite-sized pieces. Set aside.
In a large skillet, wok, or saucepan, cook or heat bacon (fat) until lightly browned on medium heat. If using bacon/pork, cut into space pieces once browned and add put back in skillet (if not done already). Add onions and stems and cook over medium heat for approximately 5 to 7 minutes until brown, stirring occasionally.
Stir in garlic. Add water to the hot pan, stirring to loosen any particles from bottom of pan. Stir in sugar and red pepper. Bring mixture to a boil.
Add the beet greens, gently toss in the onion mixture so the greens are well coated. Reduce heat to low, cover and simmer for 5-15 minutes until the greens are tender. (If substituting kale/collard greens for beet leaves, cook until desired tenderness.) Stir in vinegar.