Preheat the oven to 425°. Mix together the dressing ingredients and set aside to allow flavors to meld.
Cover a sheet pan with foil or parchment. Peel the sweet potatoes and cut into ½ inch to 1 inch cubes. Pile the potato cubes on the pan. Drizzle with olive oil, and sprinkle with salt and pepper. Toss until all pieces are coated and spread out in a single layer with a bit of space between them. Roast for 25 minutes or until a little firm on the outside and tender inside when pierced with a fork. You may see a little char on the edges and that's fine.
While the sweet potatoes roast, add the pecans to a dry skillet and warm over medium heat just until fragrant. Remove from the heat.
When the potatoes are done, allow them to cool on the sheet pan for 15 minutes.
Add the sweet potatoes, pecans, cranberries, and scallions to a large bowl. Toss gently until all ingredients are evenly distributed. Sprinkle the feta in and give another light toss. Add the dressing and toss gently again. Chill or enjoy at room temperature.