Preheat the oven to 350 degrees F (175 degrees C). Grease a baking dish with 1 tablespoon coconut oil.
Place grated sweet potatoes in the bottom of the baking dish.
Heat 2 tablespoons coconut oil in a skillet over medium heat. Add sausage and onion. Cook and stir until sausage is browned and onion is translucent, about 5 minutes. Place mixture in the baking dish on top of the potatoes.
Mix eggs, coconut milk, sage, salt, pepper, and garlic powder together in a bowl. Pour mixture into the baking pan.
Bake in the preheated oven until set, about 45 minutes.