Preheat the oven to 425°F and line a large sheet pan with parchment paper if desired.
Prepare the chicken by patting it dry with paper towels, then butterfly or cut into large, even-sized chunks so it cooks evenly.
In a small bowl or jar, combine the honey, olive oil, chili powder, garlic powder, ground ginger, salt, black pepper, and cayenne if using, and mix until smooth and well combined.
Place the sweet potatoes on one side of the sheet pan and the chicken on the other side, or spread everything evenly across the pan.
Pour the chili honey sauce evenly over the chicken and sweet potatoes, then toss everything directly on the tray until well coated.
Spread everything into a single layer so the chicken and sweet potatoes roast properly. Bake for 25 to 30 minutes, or until the chicken is cooked through, the sweet potatoes are tender, and the edges are lightly caramelized. Flip halfway through for even browning and better caramelization.
For extra flavor and a glossy finish, place under the broiler for 2 to 3 minutes until sticky and golden.
To make the cilantro yogurt sauce: finely chop the cilantro, then add it to a bowl with yogurt, lime juice, garlic powder, and salt, mix until smooth, add a splash of water if needed for a drizzle consistency, and taste and adjust seasoning.
Drizzle the chicken and sweet potatoes with the cilantro yogurt sauce (see notes). Serve sprinkled with the chopped green onions.