Combine the couscous and the boiling water in a bowl. Cover and let it rest for 10 minutes. Then, fluff with a fork, breaking up any clumps. Reserve to cool.
Brush both sides of each sweetpotato slice with olive oil and season with salt. Preheat a grill to medium-high heat. Oil the grill grates, then place the sweetpotatoes on the hot grill. Cook for 3 to 7 minutes per side, until charred and tender. Remove and let them cool, then cut into 1/2-inch cubes. Reserve.
Combine all the dressing ingredients in a dressing shaker or mason jar and shake until emulsified. Reserve.
In a large bowl, combine the sliced kale with 1/2 of the dressing. Using your fingers, massage until the kale softens and wilts, about 3 minutes. Add the couscous, diced sweetpotatoes and the remaining salad ingredients, then add the remaining dressing and toss everything until well combined.
Taste and adjust salt and pepper, then serve!