Onions are naturally sweet. When you cook onions low and slow, it brings out all the natural sugar in the onions. These Slow Cooker Sweet Caramelized Onions are great on hamburgers, hot dogs, steaks, grilled chicken, pizzas, in onion soup, and more. Slow Cooker Sweet Caramelized Onions reminds me of being a Christian.  We are not naturally sweet.