Preheat your grill.
In a large bowl, combine sweet potatoes, onion, apple, and bell pepper. Add the oil, lime juice and spices and toss well to coat evenly.
Lay two large rectangular pieces of heavy duty aluminum foil on your counter or work surface. Mound the sweet potato mixture into the middle and wrap in the foil, turning the top and side edges over on to themselves to make a tight, well-sealed package. Place foil packets directly on the grill and cook over medium heat until the vegetables are tender, about 20-30 minutes.
(Alternately, you could roast the foil packets in a 450°F oven for 45 minutes. Open up the foil packets and continue to roast until tender and starting to caramelize, about 15 minutes more.)
Remove from the grill and let cool slightly before unwrapping. Transfer to a large serving bowl and sprinkle with cashews before serving. Enjoy!