In a bowl, gently combine ground chicken, pumpkin purée, breadcrumbs, egg, grated garlic, onion powder, salt, and black pepper without overmixing.
Heat olive oil in a large skillet over medium heat.
Form the mixture into meatballs and pan-fry them until golden brown and cooked through, about 6-8 minutes, turning carefully.
Remove meatballs from skillet and set aside.
In the same skillet, melt butter over medium heat and add grated garlic and fresh sage, sautéing briefly until fragrant.
Pour in heavy cream and add salt, pepper, and optional nutmeg, simmering gently without boiling until slightly thickened.
Return meatballs to the skillet, spooning sauce over them to coat and warm through.
Serve immediately with your choice of pasta, rice, or crusty bread.