Preheat oven to 425° and cover a baking sheet with parchment paper.
Arrange sweet potatoes on a baking sheet and drizzle with 2 tablespoons of olive oil. Season with salt and pepper and toss to coat. Roast until golden and tender for about 25 minutes.
Combine quinoa and 2 cups of water in a medium saucepan and bring to a boil. Reduce heat, and simmer covered for 15 minutes. Remove from heat, and let sit covered for 5 more minutes. Scoop quinoa onto a paper towel-lined baking sheet to cool slightly.
In a large bowl, combine quinoa, sweet potatoes, red-leaf lettuce, and cranberries.
In a small bowl, whisk together the balsamic vinegar with the remaining 3 tablespoons of olive oil. Drizzle the vinaigrette over the salad and toss gently to combine. Season the salad with salt and pepper and top with feta just before serving.