Preheat the oven to 425F. Prick each potato a few times with a fork. Transfer the potatoes to a baking sheet and bake for 50-60 minutes, or until each potato is fork tender. Allow the potatoes to cool for about 15 minutes, or until they can be handled.
While the potatoes cook, place the quinoa in a fine sieve. Rinse it under running water for about a minute. Transfer it to a small saucepan and add 1 scant cup water. Bring the quinoa to a boil and then reduce heat to low. Cover and simmer the quinoa for 13 minutes. Remove the quinoa from heat, fluff it gently with a fork, and then re-cover and allow it to steam for 5 minutes.
Place the kale in a medium sized mixing bowl. Add the oil, lemon, salt, pepper, and shallot. Place the quinoa in a mixing bowl. Whisk together the oil, apple cider vinegar, mustard, agave syrup if using, salt, and pepper. Massage this dressing into the kale, until the kale is very well dressed and softening. Add the cooked quinoa, carrot, pepper, celery, and green onion. Mix well.
When the potatoes have cooled, cut them in half lengthwise and then gently scoop out most of the flesh. Chop the flesh roughly and add it to the quinoa kale mixture, along with the almonds. Stuff as much of the quinoa and kale salad as you can into each half of the sweet potato skin. Serve, along with any leftover filling.