Preheat your oven to 375°F (190°C) and lightly grease an 8x8-inch baking dish with butter or non-stick cooking spray.
Place the peeled sweet potato chunks in a large pot and cover with cold water. Bring to a boil over high heat, then reduce heat to medium and simmer for 15-20 minutes, or until the potatoes are very tender when pierced with a fork.
Drain the sweet potatoes thoroughly in a colander and return them to the warm pot. Mash them with a potato masher or fork until smooth with no large lumps remaining.
Add the Greek yogurt, melted butter, warm milk, salt, pepper, and garlic powder to the mashed sweet potatoes. Stir vigorously with a wooden spoon until the mixture is completely smooth and well combined.
Stir in the lightly beaten egg until fully incorporated into the sweet potato mixture, which will help create a light and fluffy texture when baked.
Transfer the mixture to the prepared baking dish and spread it into an even layer. Drizzle the top with maple syrup and sprinkle evenly with chopped pecans.
Bake for 25-30 minutes, or until the edges are lightly bubbling and the top is golden brown. Let the bake rest for 5 minutes before serving to allow it to set.