Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

In a large mixing bowl, combine ground turkey, pumpkin puree, breadcrumbs, Parmesan cheese, beaten egg, chopped onion, minced garlic, sage, salt, pepper, nutmeg, and red pepper flakes. Mix gently until just combined.

Shape the mixture into balls about 1 to 1.5 inches in diameter and place them on the prepared baking sheet.

Heat a skillet over medium-high heat and add olive oil. Sear the meatballs for about 3-4 minutes per side until golden brown.

Transfer the meatballs to the baking sheet and bake for 15-20 minutes or until the internal temperature reaches 165°F (74°C).

Let the meatballs rest for a few minutes before serving, garnished with sage or Parmesan if desired.