Light your grill and set it up for two zone cooking, establishing temperature at 400°F as indicated by a reliable leave-in thermometer.
While your grill is coming up to temperature, whisk together all ingredients for the seasoning, breaking up any clumps of brown sugar.
In a large mixing bowl, toss the sweet potatoes with olive oil. Sprinkle one quarter of the seasoning on top of potatoes and toss. Repeat until potatoes are evenly coated (you may not use all the seasoning depending on the size of your potatoes), then transfer to a parchment paper lined baking sheet.
Place the baking sheet on the grill grate (or in the oven) over indirect heat. Close the lid and let the potatoes roast at 400°F for 30 minutes. While potatoes are roasting, make the avocado cilantro cream.
In a small bullet style blender or food processor, add all ingredients for cream and blend until smooth. Taste and adjust salt to your liking, set aside. Finely chop two tablespoons of cilantro.
Using a fork, check to be sure the potatoes are tender by piercing them. The fork should go in with little resistance. Remove the roasted potatoes from the grill; plate and serve with avocado and cilantro cream.