Preheat oven to 400°F/200°C
Cut the sweet potatoes in half lengthwise. Brush the tops and skins with olive oil and place them cut-side down on a baking sheet lined with parchment paper. Place sweet potatoes in the oven for 40 minutes or until completely tender.
Meanwhile, cook the quinoa: In a medium saucepan, bring quinoa, water, and ¼ teaspoon salt to a boil. Reduce heat to low, cover, and cook for 15-20 minutes until the water has been absorbed and the quinoa is tender. Allow to cool to room temperature.
In a medium bowl, combine cooked quinoa, garlic, olive oil, lemon juice, dried cranberries, 1/2 teaspoon salt, and pepper. Gently add the feta into quinoa mixture.
When the sweet potatoes are ready and still warm, gently press the center with a spoon to create an indentation. Spoon quinoa mixture evenly over sweet potatoes. Serve while sweet potatoes are still warm.