1. Preheat the oven to 400 degrees . Place sweet potatoes on a rimmed baking sheet lined with aluminum foil and bake until soft, 60 to 70 minutes.
2. When sweet potatoes have about 15 minutes left to cook, heat oil in a large skillet over medium-high heat. Add garlic and ginger and cook until fragrant but not browned, 30 seconds to 1 minute. Add curry powder and cook until fragrant, 15 to 30 seconds. Add tomatoes, coconut milk, brown sugar, vinegar and salt and bring to a simmer, scraping up any spices from bottom of skillet. Add spinach and cook, stirring occasionally, until bright green and wilted, about 3 minutes. Stir in chickpeas and cook until heated through, 1 to 2 minutes.
3. Split sweet potatoes down the middle and push sides to open them up. Stir chopped cilantro into chickpea mixture and ladle over sweet potatoes. Garnish with cilantro leaves if desired.