In a small bowl, whisk the coconut oil, syrup, cinnamon, and salt. Put the potato and peaches in 2 separate bowls. Put three-quarters of the syrup mixture over the sweet potato and one-quarter over the peaches and toss. Spread the potato in an even layer in a large baking dish and roast for 10 minutes. Toss the potato and roast for 5 minutes more. Add the onion and roast for 15 minutes. Toss the potato and onion, add the peaches in an even layer, and roast 10 minutes, or until the potato and onion are fork tender and the peaches have caramelized.