Add 4 tbsp water to a large skillet along with the onion slices. Cook over medium heat, stirring occasionally until the water has evaporated and the onions are beginning to brown on the bottom of the pan (about 8 minutes).
Add another 4 tbsp of water to the pan along with peaches and oregano and let the water cook off again, stirring occasionally. The onions should be nicely browned and caramelized and the peaches will be slightly soft.
Blend the roasted garlic, vinegar, salt and pepper together in a small bowl to make dressing.
Bring a small saucepan of water to a boil (about 6 quarts). Add green beans and boil for 2 minutes. Strain and place in a bowl of ice water to stop the cooking process.
Toss green beans together with onion peach mix and the garlic dressing. Serve and enjoy!