Preheat your oven to 400 degrees F. Toss the butternut squash in the oil and place on a baking sheet. Roast for 20-30 minutes until the squash pierces easily with a fork. Remove from oven, mash with a fork, and set aside.
In a large pot, melt the butter over medium heat. Add onion; cook and stir for 2 minutes until the onion begins to soften, then stir in the rice. Continue cooking and stirring until the rice is glossy from the butter, and the onion begins to brown on the edges, about 5 minutes more. Add the minced garlic.
Pour in the white wine; cook, stirring constantly, until it has evaporated. Stir in broth 1/3 cup at a time, until the chicken stock has been absorbed by the rice, which will take a few minutes per addition.
Finish by stirring in the Parmesan cheese, and seasoning to taste with salt and pepper. Stir in the squash.