In a large skillet over medium-high heat, heat the oil or melt the butter. Add the cumin seeds and chili powder and cook, stirring, until fragrant, about 30 seconds.
Add the sweet potatoes and brown sugar. Season with salt and pepper. Cook, stirring occasionally, until the sweet potatoes are tender and caramelized, about 10 minutes. Remove from heat.
Stir in the chopped cilantro and serve.
