Heat a large sauce pan or Dutch oven over medium high heat. Add the olive oil and swirl to coat the bottom of the pan.
Add the onion and butternut squash and sauté until the onion is softened and the squash has browned slightly.
Add the rice, garlic, and sage and stir. Add the stock 1 cup at a time, stirring and allowing the liquid to be absorbed before adding more liquid. Once all of the stock has been added, add the spinach, black pepper, and cheese and stir well. Adjust the seasoning with salt and pepper and serve hot topped with the red bell pepper.