In a large mixing bowl, combine ground chicken, canned pumpkin purée, plain breadcrumbs, egg, finely grated garlic, onion powder, salt, and black pepper. Gently mix the ingredients together until just combined.

Using damp hands or a cookie scoop, form the mixture into 1.5-inch meatballs and place them on a parchment-lined baking sheet.

Heat a nonstick skillet over medium heat and add a drizzle of olive oil. Once shimmering, add the meatballs and cook for about 2-3 minutes on each side until golden brown.

In a small saucepan, melt 2 tablespoons of unsalted butter over medium heat. Add the finely chopped sage and grated garlic, stirring for about 30 seconds until fragrant.

Slowly pour in the heavy cream, and add a pinch of salt, black pepper, and nutmeg if desired. Stir and allow to simmer gently for 3-4 minutes until thickened.

Transfer the browned meatballs to the saucepan with the simmering sage cream sauce. Stir gently to coat and simmer for an additional 5-7 minutes.

Serve the meatballs in shallow bowls, garnished with additional sage leaves and a sprinkle of black pepper.