Place the peeled and diced sweet potatoes in a colander and rinse them with water.
Dump them into a large bowl and toss with the olive oil, cinnamon, nutmeg, allspice. Place them in a single layer on a rimmed baking sheet.
Roast at 400 F for 25-35 minutes, or until all are soft. Roasting time may vary depending on thickness of the sweet potato pieces. Remove from oven and let cool.
In a small mixing bowl, whisk together the honey, mustard, and mayo. Stir in the basil leaves. Pour the dressing over top of the sweet potatoes.
Serve warm, or chill for at least 2 hours and serve chilled.