Arrange the sweet potatoes on a large baking sheet in a single layer and toss with just olive oil to lightly coat. Sprinkle with salt and pepper and roast until lightly browned and soft, tossing once or twice, 30-45 minutes.
To make the dressing, combine 3 tablespoons olive oil, orange juice and zest, maple syrup, salt, and cinnamon if using. I like to stick it in a mason jar and shake, or you could whisk it all together in a small bowl.
To arrange the salad, divide kale, onion, goat cheese, walnuts, and sweet potato amongst four plates. Drizzle dressing over the top and serve.