Soak beans for at least 8 hours or overnight, rinse and follow cooking instructions. Sauté the onions with olive oil for 5 minutes over medium heat. Add the sugar and sauté another 7 minutes. Increase heat to high for 2 minutes.
In a separate pan, cook the peaches over medium heat for 10 minutes, adding small amounts of water if the liquid from the peaches dries completely. Combine peaches and onions. Add lime juice.
Serve the taco with a layer of the cooked peach mixture, a layer of beans, and some lettuce. Garnish with pomegranate seeds.