Heat oven to 450°F and line a baking sheet with parchment paper. Toss sweet potatoes with 3 tablespoons olive oil and sprinkle generously with salt and pepper. Spread in an even layer on the baking sheet and roast until tender, about 20-25 minutes depending on how big they are.
Meanwhile, heat remaining 3 tablespoons oil in a large frying pan over medium heat. Add remaining ingredients and season with salt and pepper. Cook until fragrant, about 1-2 minutes. Reduce heat to low and continue cooking until ginger is soft, about 15-20 minutes more.
Remove sweet potatoes from oven, transfer to a serving dish, top with garlic mixture and serve.