Add the ground chicken, pumpkin purée, breadcrumbs, egg, grated garlic, onion powder, salt, and black pepper to a large mixing bowl. Gently mix until the ingredients are evenly combined. Avoid overmixing.
Lightly wet your hands and shape the chicken mixture into approximately 16 meatballs, each about 1½ inches in diameter.
Heat the olive oil in a large skillet over medium heat. Add the meatballs, leaving a little space between them. Brown for about 2–3 minutes per side, turning carefully until golden on the outside.
In a separate saucepan or clean skillet, melt the butter over medium heat. Add the minced garlic and chopped fresh sage. Cook for about 30 seconds, stirring frequently, until fragrant.
Pour in the heavy cream. Season lightly with salt and black pepper, then reduce the heat and gently simmer for 3–4 minutes.
Transfer the browned Pumpkin Chicken Meatballs into the creamy sage sauce. Turn them gently so they are coated on all sides.
Simmer for another 5–7 minutes, or until the meatballs are completely cooked through and reach an internal temperature of 165°F (74°C).
Spoon the meatballs and creamy sage sauce into shallow bowls. Finish with fresh sage and freshly ground black pepper before serving.