Place a steaming basket in a large pot filled with ½” or so of water. Bring to a boil.

Prep sweet potatoes: Peel, trim ends, and cut in half lengthwise. Cut each sweet potato half into ½” thick slices. Add the sweet potatoes to the steaming basket, cover, and cook until sweet potatoes are just-tender, 4 to 5 minutes. The skewer should easily pierce the sweet potato but not cause it to fall apart.

Transfer the sweet potatoes to a bowl and toss with olive oil, spices, and salt. Let cool enough to handle.

Light grill to medium heat. Cut onions into pieces similar in size to the sweet potatoes. Alternate sweet potatoes and onion slices on skewers.

Place skewers on grill and cook, turning occasionally, until sweet potatoes have lightly charred on all sides, 8 to 10 minutes.

While the skewers are grilling, combine the ingredients for the dressing in a blender. Puree until smooth and there are no large pieces of cilantro.

Serve skewers over grains with a solid drizzle of the dressing and extra cilantro if desired.