Start by peeling, seeding, and cubing the pumpkin, then set it aside.
Chop the onion finely and mince the garlic cloves to prepare for sautéing.
Add the olive oil to the slow cooker and turn it on to low heat, then pour in the chopped onion and minced garlic. Sauté gently for about 5 minutes until fragrant and slightly translucent.
Stir in the cubed pumpkin, Arborio rice, ground nutmeg, and chopped sage, ensuring the rice is well coated with the aromatic mixture.
Pour the warm vegetable broth over the ingredients, season with salt and pepper, then cover the slow cooker with its lid.
Set the slow cooker to low and cook for 2 hours, stirring once or twice during cooking to prevent sticking, until the rice is tender and the pumpkin has softened into a creamy sauce.
Once done, uncover the slow cooker and give the risotto a gentle stir; its texture should be creamy and the pumpkin uniformly blended.
Taste and adjust seasoning with additional salt, pepper, or sage as desired for added flavor.
Scoop the warm pumpkin risotto into bowls, optionally garnished with fresh herbs or a drizzle of olive oil for a beautiful presentation.